Include manage_connector privilege in generated api keys

[jedrazb]

Closes https://github.com/elastic/search-team/issues/7837

We introduced manage_connector privilege in ES: elastic/elasticsearch#110128

Let's use it for new generated API keys for connectors.

See Kibana PR for reference with similar change: elastic/kibana#187361

This is not backward compatible, since the new privilege is introduced in 8.15. Hence CLI won't work with <8.15 ES versions

Checklists

Pre-Review Checklist

• this PR does NOT contain credentials of any kind, such as API keys or username/passwords (double check config.yml.example)
• this PR has a meaningful title
• this PR links to all relevant github issues that it fixes or partially addresses

[github-actions]

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