Initial sample data for geospatial data ingest blog (#337)

* Initial sample data for geospatial data ingest blog

* Added sample data for drone flights

* Restructured to sub-directories

* Fix links

supporting-blog-content/geospatial-data-ingest/README.md

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+## Geospatial data ingest for ES|QL
+
+This folder contains sample data used in various blogs about querying
+Geospatial data using ES|QL. In particular:
+
+* [Geospatial data ingest for ES|QL](https://www.elastic.co/search-labs/blog/geospatial-data-ingest)
+* [Geospatial search with ES|QL](https://www.elastic.co/search-labs/blog/esql-geospatial-search-part-one)
+* [Geospatial distance search with ES|QL](https://www.elastic.co/search-labs/blog/esql-geospatial-search-part-two)
+
+Most of the data we used for the examples in these blogs were based on data we use internally for integration tests.
+But some data was generated by the authors:
+
+* [airports](airports/README.md)
+* [drone](drone/README.md)
+
+Each of these sets of data has different licensing requirements depending on
+the original data sources. Please read the included README in each
+directory for specific attribution and other licensing requirements.

supporting-blog-content/geospatial-data-ingest/airports/README.md

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+## Geospatial data ingest for ES|QL
+
+This folder contains sample data used in the blogs:
+
+* [Geospatial data ingest for ES|QL](https://www.elastic.co/search-labs/blog/geospatial-data-ingest)
+* [Geospatial search with ES|QL](https://www.elastic.co/search-labs/blog/esql-geospatial-search-part-one)
+* [Geospatial distance search with ES|QL](https://www.elastic.co/search-labs/blog/esql-geospatial-search-part-two)
+
+The data we used for the examples in these blogs were based on data we use internally for integration tests.
+This in turn was created by merging data from a few different souces with
+the goal of creating datasets appropriate for testing a number of specific
+ES|QL features as they were developed.
+
+* [airports.csv](https://raw.githubusercontent.com/elastic/elasticsearch-labs/tree/main/supporting-blog-content/geospatial-data-ingest/airports/airports.csv)
+  * This contains a merger of three datasets:
+    * Airports (names, locations and related data) from [Natural Earth](https://www.naturalearthdata.com/downloads/10m-cultural-vectors/airports/)
+    * City locations from [SimpleMaps](https://simplemaps.com/data/world-cities)
+    * Airport elevations from [The global airport database](https://www.partow.net/miscellaneous/airportdatabase/)
+* [airport_city_boundaries.csv](https://raw.githubusercontent.com/elastic/elasticsearch-labs/tree/main/supporting-blog-content/geospatial-data-ingest/airports/airport_city_boundaries.csv)
+  * This contains a merger of airport and city names from above with one new source:
+    * City boundaries from [OpenStreetMap](https://www.openstreetmap.org/)
+
+### Licensing and attribution
+
+Since this data is derived from various sources, we list the license
+conditions for each, some of which also require attribution:
+
+* Natural Earth (original dataset with airport names, locations and related
+  information)
+  * Released in the public domain with no requirement for attribution. See
+  https://www.naturalearthdata.com/about/terms-of-use/.
+* SimpleMaps (city locations)
+  * License: Creative Commons Attribution 4.0 license as described at: https://creativecommons.org/licenses/by/4.0/
+  * Requires attribution and link to https://simplemaps.com/data/world-cities
+* Global Airport Database (airport elevations)
+  * Licensed under MIT license - http://www.opensource.org/licenses/MIT
+  * Requires attribution: https://www.partow.net/miscellaneous/airportdatabase/
+* OpenStreetMap (city boundary polygons)
+  * Licensed with Open Database License (ODbL) v1.0 - https://opendatacommons.org/licenses/odbl/1-0/
+  * Requires attribution
+  * Requires that derived data be shared under a compatible license
+
+The most restrictive license here is the [Open Database License (ODbL)
+v1.0](https://opendatacommons.org/licenses/odbl/1-0/) because it as a
+'ShareAlike' clause. For this reason we are sharing this combined dataset
+using the same license.
+
+### Changes made to the data
+
+Several of the above licenses also require that any changes made from the
+original source data are clearly indicated. This can be done by explaining
+the process used to create the final results:
+
+* The original airports name, IATA code, location, type and scalerank were
+  obtained from the Natural Earth dataset. The only changes made were to
+  reformat into a CSV format, with the locations expressed in WKT, since the
+  original format was ESRI Shapefile.
+* The city locations from SimpleMaps were download and then only the subset
+  of cities reasonably identifiable as the closest major city to one of the
+  existing airport locations was selected and merged into the airports.csv
+  file. So the edit in question is simply a subset selection.
+* The airport elevations were similarly a subset selection of airports from
+  the 'global airport database' where IATA codes matched the existing set of
+  airports in our dataset.
+* The city boundaries were found from OpenStreetMap. The process to
+  determine the boundaries was complex, for many reasons including the fact
+  that OSM data is massive. We downloaded OSM.PDB files for various regions of
+  the world from the Geofabrik download server at
+  https://download.geofabrik.de/. For each region we imported the PDF files
+  into PostGIS, and then searched for appropriate polygons surounding cities
+  serving the airports of interest. This was achieved using several complex
+  SQL queries. The selected polygons were further simplified using
+  `ST_SimplifyPreserveTopology` calls with various resolutions to generate
+  city polygons of appropriate levels of detail.