Add a few more swagger descriptions and examples.

[fisx]

Checklist

• [X] Add a new entry in an appropriate subdirectory of changelog.d
• [X] Read and follow the PR guidelines

[mastaab]

can you maybe also add a description for "currency" while you are at it?

[netbe]

out of curiousity, where does the retention_information link go to ? @fisx

[fisx]

out of curiousity, where does the retention_information link go to ? @fisx

the code that parses asset ids :-)

but as @akshaymankar says, it's probably better to take that out again.

[fisx]

after.json before.json diff.json