Fields with enabled time_series_dimension don't support multi values in non tsdb index modes

[felixbarny]

For OTel mappings, we're using a common definition of attributes and resource attributes for logs, metrics, and traces to avoid duplications and ensure a consistent mapping:

elasticsearch/x-pack/plugin/otel-data/src/main/resources/component-templates/[email protected]

Lines 20 to 24 in 73c5c1e

	attributes:
	type: passthrough
	dynamic: true
	priority: 10
	time_series_dimension: true

elasticsearch/x-pack/plugin/otel-data/src/main/resources/component-templates/[email protected]

Lines 9 to 15 in 73c5c1e

	resource:
	properties:
	attributes:
	type: passthrough
	dynamic: true
	priority: 30
	time_series_dimension: true

That's why we set time_series_dimension to true which I had expected to only kick in for TSDB data streams and ignored for others. However, it seems like a validation gets kicked in which disallows attributes to have multiple values (due to #110387), even in standard and logsdb index modes. As a result, this exception is thrown:

elasticsearch/server/src/main/java/org/elasticsearch/index/mapper/DocumentDimensions.java

Line 103 in 73c5c1e

throw new IllegalArgumentException("Dimension field [" + fieldName + "] cannot be a multi-valued field.");

I think the reason for that is that even for IndexMode.STANDARD, we return an implementation of DocumentDimensions that only allows single values:

elasticsearch/server/src/main/java/org/elasticsearch/index/IndexMode.java

Lines 107 to 109 in 73c5c1e

	public DocumentDimensions buildDocumentDimensions(IndexSettings settings) {
	return new DocumentDimensions.OnlySingleValueAllowed();
	}

Maybe we should return a noop implementation for index modes standard and tsdb? Or silently ignore time_series_dimension when the index mode is not tsdb.

We can also discuss other options for how we can compose our mappings so that multi-valued attributes are allowed for logs and traces while ensure consistency across the mappings and not having to duplicate mappings (in particular the ECS alias mappings, which are quite long)

cc @elastic/obs-ds-intake-services @gregkalapos

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)