Avoid sending bulk requests larger than bulk_limit_bytes

What does this MR do?

Update the Elasticsearch bulk indexer to work towards resolving #211597 (closed). A similar change needs to be made to the go indexer.

The current behaviour of BulkIndexer is to send a bulk request as soon as the request body is larger than bulk_limit_bytes. This MR proposes that a bulk request should be sent before adding a document, if adding it would result in the request size being greater than bulk_limit_bytes.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team