[Feature Anywhere] [Enhancement] Support plugin-granular settings

[ohltyler]

Coming from #2880

For the initial release of the feature, we plan to have a single advanced setting to toggle all plugin integration with visualizations (see #3361). As more plugins onboard, and to give the admin more control, we should support a more granular level of feature enablement in the future. For example, enabling at a per-plugin level, where integration may be enabled for anomaly detection, but disabled for alerting and forecasting, etc.

Listing a few brainstorming implementation ideas below:

• enforce a "registration" from the vis augmenter plugin that can be used to keep track of what plugins are enabled / available to use the feature
• dynamically add settings for each of these "registered" plugins
• handle logic to add/remove settings upon startup when plugins are registered / de-registered from the plugin. saved object migration of the advanced settings saved object types may help with this.
• using the "registered" plugins concept, we can simplify/control the menu options in the vis menu - for example, rather than plugins registering an action to add a menu item, the vis augmenter can handle it by automatically creating one for each "registered" plugin