I think the behavior specified in IndexAliasesIT#testIndicesGetAliases is wrong. Namely:

• create indices foobar, test, test123, foobarbaz, bazbar
• add an alias alias1 -> foobar
• add an alias alias2 -> foobar
• execute get aliases on the transport layer specifying alias1 as the only alias to get
• the response includes foobar, test, test123, foobarbaz, bazbar albeit with empty alias metadata for all indices except foobar which contains alias1 only
• previously the response would only contain foobar with alias metadata for alias1

This was a breaking change resulting from #25114, the specific change in behavior arising from a change to MetaData.

I am opening this personally considering it a bug but for discussion where we might decide to only document this behavior (not my preference, I think this behavior is weird and not intuitive).

Relates #27743