feat(datastore): add support for request tags

[rahulmane-goog]

• Add RequestOptions support that enables ability of passing request tags to Datastore queries.
• Introduced instance level request tags in the DatastoreOptions.
• Introduced the logic of populating RequestOptions for all datastore queries. These are query level tags.
• Introduced overloaded run(...) and runAggregation(...) client methods, that pass RequestOptions proto as the last parameter.
• The instance and query level tags are combined using the new RequestOptionsHelper utility and sent inside the query requests.

[gemini-code-assist]

Code Review

This pull request introduces support for passing and merging RequestOptions (such as request tags) in Datastore queries and aggregation queries, allowing both instance-level and request-level tags to be propagated. The feedback highlights a critical issue where instance-level tags are ignored when query-level RequestOptions are not explicitly provided in QueryResultsImpl and AggregationQueryRequestProtoPreparer. Additionally, the reviewer suggests simplifying the varargs withRequestTags overload in Datastore by delegating to the List version, and adding a test case to verify that instance-level tags are correctly populated and sent with queries.

[rahulmane-goog]

Please review

[jinseopkim0]

ci / lint is failing. Could you please take a look?

[rahulmane-goog]

ci / lint is failing. Could you please take a look?

Fixed