Add ability to tag runs

[johnstairs]

Like with buffers, you can now assign tags to runs.

tyger run create [...] --tag a=1

tyger run set ID [--clear-tags] --tag b=2 [--etag CURRENT_ETAG]

You can filter runs by tags:

tyger run list --tag a=1,b=2

And display counts filtered by status:

tyger run count --tag a=1,b=2

You can also filter by status:

tyger run list --tag a=1 --status failed,canceled

Tags and ANDded together, statuses are ORed.

You can watch the tags change until a run completes with tyger run watch ID --full-resource

[hansenms]

Looks good. Minor stuff in the docs.