Remove escaping from external compaction entries in metadata table

[keith-turner]

Is your feature request related to a problem? Please describe.

External compaction entiries in the metadata table are json and include the files that are being compacted. The files in the json are also json and when added to the outer json as values are escaped.

Describe the solution you'd like

Not sure if its possible, but it would be nice to remove the escaping for the file entries if possible.

Describe alternatives you've considered

Could do nothing, the escaping is very unpleasant to look at when scanning he metadata table but its not hurting anything. The escaping may make using tools like jq w/ the data a bit harder also.

[cshannon]

I took a look at this and was thinking a bit about it and the only really good way to get rid of the escaping would be to not use the serialized json string of the files and instead use an object representation of StoredTabletFile, but that would break the encapsulation of StoredTabletFile and expose the file/range outside of it so I'm not sure if that's a great idea. A custom serializer would be tricky because escaping quotes are needed so it's valid json.

I'm wondering if this is something that is better solved as custom logic when scanning and logging to print it out in an easier to read format vs storing it differently.