Update solution docs to include applies_to versions

[mdbirnstiehl]

Some of the observability solutions docs don't specify versions in the applies_to front matter, need to make sure these are all GA, or if they need to be updated.

[florent-leborgne]

Note: it's ok not to specify versions. Good defaults are:

stack: ga (or any other lifecycle status) -> That means the feature is GA and applies to all versions currently released since 9.0
stack: all -> Does kind of the same and renders the same way as above except that it takes the "version" angle and omits the lifecycle.

I'd prefer to go with the first option whenever possible for pages that just need a default value.