Replace bindata packages with stdlib go:embed.
Modernize some uiserver code with newer interfaces introduced in go 1.16 (mainly working with fs.File instead of http.File.
Remove steps that are no longer used from our build files.
Add Github Action to detect differences in agent/uiserver/dist and verify that the files are correct (by compiling UI assets and comparing contents).
I noticed that the JSON api endpoints for peerings json encodes protobufs directly, rather than converting them into their `api` package equivalents before marshal/unmarshaling them.
I updated this and used `mog` to do the annoying part in the middle.
Other changes:
- the status enum was converted into the friendlier string form of the enum for readability with tools like `curl`
- some of the `api` library functions were slightly modified to match other similar endpoints in UX (cc: @ndhanushkodi )
- peeringRead returns `nil` if not found
- partitions are NOT inferred from the agent's partition (matching 1.11-style logic)
