[Add] Add integration syncing troubleshooting section to remote ES output doc

[jillguyonnet]

Closes elastic/kibana#208946

This PR updates the documentation about remote Elasticsearch outputs with:

• a mention of the feature to sync uninstalled integrations
• a new troubleshooting section

Screenshots

[jillguyonnet]

Hi @juliaElastic @criamico This is a first draft based on my current understanding and UI designs. Please let me know if I left anything out.

@kilfoyle FYI while this is in draft.

[criamico]

Should we mention that the remote cluster needs to have an elasticsearch output configured matching the remote_elasticsearch output in the main one? I recall some discussion about it but I don't know what was the outcome.

If this condition is necessary to kickstart the sync, I think it should be mentioned in the troubleshooting section.

[jillguyonnet]

Should we mention that the remote cluster needs to have an elasticsearch output configured matching the remote_elasticsearch output in the main one? I recall some discussion about it but I don't know what was the outcome.

I had asked the same question in #952 (comment). As I understand, the default output takes care of that as its host URL should match that of the remote output, so there is no further action needed from the user. In our local dev setup, we need to alter the port of the default output to make it work, but this seems like a very specific case.

[juliaElastic]

I had asked the same question in #952 (comment). As I understand, the default output takes care of that as its host URL should match that of the remote output, so there is no further action needed from the user. In our local dev setup, we need to alter the port of the default output to make it work, but this seems like a very specific case.

Yes the default ES output should take care of this, we could mention it in the docs, something like: "Check that the remote Elasticsearch host is correct (should match one of the Elasticsearch hosts on the remote cluster)"

[juliaElastic]

LGTM

[kilfoyle]

LGTM! ⛵
Just a few super minor suggestions. Thanks a lot @jillguyonnet for adding these nice docs!