[Ingest Manager] Support for multiple kibana urls

[neptunian]

#72731

Changes

• the kibana configuration xpack.ingestManager.fleet.kibana.host now accepts both a string url or an array of string urls.
• the Kibana URL in the settings flyout is now a EUI combo box that allows for multiple URLS

• the ingest_manager_settings saved object's kibana_url attribute is now an array of strings type
• the PUT /api/ingest_manager/settings was changed from allowing only a string url to allowing only an array of string urls. GET always returns kibana_url as an array of strings.

TODO / Questions

• validate yaml input and UI so only the hostname can differ in the urls
• can the elastic agent cli be modified to accept a comma separated list of hosts? Currently the array of urls is being passed through and shown in the command for the user. Otherwise we can just pick the first or random url from the array.

- if the user updates the urls, the agent doesn't know? (I think I understood this from @nchaulet)

[neptunian]

closed for #75712

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: abc8028

Build metrics

async chunks size

id	value	diff	baseline
ingestManager	1.1MB	+197.0B	1.1MB

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@elasticmachine merge upstream