Add check for GCS file upload exist

[chowbao]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with the jira ticket associated with the PR.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated the README with the added features, breaking changes, new instructions on how to use the repository. I updated the description of the fuction with the changes that were made.

Release planning

• I've decided if this PR requires a new major/minor/patch version accordingly to
  semver, and I've changed the name of the BRANCH to release/_ , feature/_ or patch/* .

What

Adding a check to see if the stellar-etl exported data file was actually upload and exists in GCS by checking for the file in GCS.

Why

There have been times that the stellar-etl task in airflow has failed to upload a file to GCS and did not fail the task. This should prevent that scenario from happening again.

Known limitations

It is in theory a redundant check but performance impact is negligible

[chowbao]

Need to test after logging issue is fixed in Airflow

[amishas157]

This looks good.
nit suggestion: To also verify size of the file is > 10b or something to ensure file is not empty

But defer to you whether that's really needed or not

[chowbao]

This looks good. nit suggestion: To also verify size of the file is > 10b or something to ensure file is not empty

But defer to you whether that's really needed or not

Actually the files can be empty in the case there is no record for a time range 😅
Example:
https://console.cloud.google.com/storage/browser/_details/us-central1-test-hubble-43c3e190-bucket/dag-exported/scheduled__2024-07-25T00:00:00%2B00:00/changes_folder/708319-708382-claimable_balances.txt;tab=live_object?project=test-hubble-319619

[amishas157]

Actually the files can be empty in the case there is no record for a time range 😅

Alright, then i take my nit suggestion back