Add Elastic Api Version header

[kaisecheng]

This commit adds "Elastic-Api-Version" : "2023-10-31" to request header when the Elasticsearch is serverless

[jsvd]

inspecting the request done by the manticore adapter in the ES ruby client, we can see the header is not being sent to the server.
a simple test is to bump the date to 2024 and confirm that we can still query a serverless deployment.
My suspicion is around header handling between the headers passed during client creation vs headers passed at request time.

[kaisecheng]

Good catch! The client got headers but completely ignored and overwritten by initial headers. It seems a bug only in manticore implementation as faraday and curb do a merge with the input headers.

[kaisecheng]

link the upstream issue elastic/elastic-transport-ruby#66

[kaisecheng]

upstream has merged the fix. We are now waiting for the release of new version

[jsvd]

minor code style fixes. Tested and works great. Would love to not have to have this add_headers constantly, but requires deeper refactoring.
LGTM

[kaisecheng]

@jsvd The last commit recreated the client with header. es-input should be straightforward to replace the client

[jsvd]

LGTM

[kaisecheng]

link the issue for cleaning up resources #196