Create a new content index if it doesn't exist

[vidok]

This PR brings back the original functionality that creates content indices.

This handles a use-case when customers use Connectors without Kibana.

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[wangch079]

I see you mentioned
https://github.com/elastic/connectors-python/blob/6b700bcdbc80e0344dc4b809db9491657df0e3fa/connectors/es/sink.py#L670

Do you want to handle mapping changes here? In normal cases, the index should be created by either Kibana or Connector service. If we find a discrepancy, should we 1) create a new index with the correct mapping or 2) raise an error or 3) simply log a warning message and continue?

[vidok]

Good question:

If the connector can't apply mappings to the index it should fail immediately. This can already happen, see this issue.

I guess it would be nice to handle it and pass a human-readable error. Is this what you also meant?

[artem-shelkovnikov]

Looks good, left a couple suggestions for log lines.

I personally find log lines ending with "..." suitable only for lines that imply some lengthy process after, e.g:

Creating something...
Created!

[github-actions]

💔 Failed to create backport PR(s)

The backport operation could not be completed due to the following error:
There are no branches to backport to. Aborting.

The backport PRs will be merged automatically after passing CI.

To backport manually run:
backport --pr 1668 --autoMerge --autoMergeMethod squash