Add support for metadata to test server

[Quinn-With-Two-Ns]

This PR does a few things:

• Add support for metadata to test server
• Add summary and detail to describe
• expose root execution

closes:

• Test Server: Add support for user metadata #2219
• Expose static summary/details on workflow execution description #2432
• Expose root workflow execution #2430

[Quinn-With-Two-Ns]

This is a bit awkward since this can only be null on old servers that didn't have this value.

[cretz]

Makes sense, may be worth documenting that here in the javadoc. I do appreciate that this is not using Optional.

[cretz]

Minor things, nothing blocking

[cretz]

Makes sense, may be worth documenting that here in the javadoc. I do appreciate that this is not using Optional.

[cretz]

Might consider memoizing this (e.g. backed by an AtomicReference). If not, at least worth clarifying in the javadoc each invocation does data conversion.

[Quinn-With-Two-Ns]

We generally don't ever memoize conversion for these type of things, same for memo. I'll note in the docs

[cretz]

I wonder if it's worth a more generic implementation of command-to-event user metadata propagation like server instead of the only known current use cases. This would make it more future proof. I understand it'd change the code a bit since there is no generic place where an event is created from a command nor is there a common place to affect an event after it is created. Up to you.

[Quinn-With-Two-Ns]

Yeah possibly, child workflow would still need some special logic, but yeah this should be generic