Monitoring plugin elasticsearch config deprecations

[jportner]

There are several config settings that are deprecated as of 7.16 and show up in the upgrade assistant:

• elasticsearch.username: elastic

  • 51101

• elasticsearch.username: kibana

  • 81680

• elasticsearch.ssl.certificate without elasticsearch.ssl.key and vice versa

  • 81746

These are not breaking in 8.0, but we want the deprecations to show in the Upgrade Assistant in 7.16 to encourage users to fix their configs. I updated these deprecation warnings for Core in #115241.

The Monitoring plugin inherits these "root" settings by default, or they can be set separately for Monitoring using the monitoring.ui. prefix. Unfortunately, while working on the PR linked above, I discovered that any issue with the root settings would surface twice in the Upgrade Assistant -- once from Core, and once from the Monitoring plugin.

To ensure that the Upgrade Assistant experience in 7.16 isn't confusing, I removed these deprecations from the Monitoring plugin (see https://github.com/elastic/kibana/pull/115241#discussion_r730151794).

The deprecations should be added again in the Monitoring plugin, but they should only show up if the Monitoring plugin is not inheriting the root settings from Core.

https://github.com/elastic/kibana/blob/b7577b5695eebf8e62f151bad7559bc59c346804/x-pack/plugins/monitoring/server/deprecations.ts#L64-L69

This is not imperative for the 7.16 release, it can be done in the 8.x timeframe.

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)