Copy as "grpcurl"

A slick feature would be to be able to `Copy as 'grpcurl'` -- which would extract all connection info from command-line flags as well as the request metadata and data in the web form and use that to generate an equivalent `grpcurl` command.

Similarly, the ability to paste a `grpcurl` command, and have that auto-populate the metadata and request message data would be slick as well.

Start by tracing how command-line flags, request metadata, and request message data from the web form are represented. Define the Copy as "grpcurl" flow and the reverse paste flow, then verify that both preserve the connection information, metadata, and request data described in the issue.

Written by the indexing model from the issue text.