Add parsing for InternalAdjacencyMatrix aggregation

[cbuescher]

This adds parsing and related tests to the InternalAdjacencyMatrix aggregation.
Based on #24698 which should go into master first.

[javanna]

left a small comment, LGTM otherwise

[javanna]

there's a typo in the name: rename to ParsedAdjacencyMatrix ?

[tlrx]

LGTM, I left some comments

[tlrx]

I think you can use the ParsedMultiBucketAggregation.ParsedBucket#toXContent() method and not declare it here again?

[cbuescher]

Yes, you are right, although this has the potential to render a keyed response or the key_as_string field if this class is not used correctly, but I guess its worth it.

[tlrx]

I agree

[tlrx]

extra lines

[tlrx]

I think you could use
return parseXContent(parser, false, ParsedBucket::new, (p, bucket) -> bucket.key = p.text());

[cbuescher]

Yes, again I used a modified method here to not parse a.g. KEY_AS_STRING but I think its worth the saving to just reuse the more general super class method since we know the response doesn't contain certain fields.

[tlrx]

I agree too