Add execute sql boiler impl

[rylev]

Adds the boiler plate code for calling (as of yet non-existent) endpoint in nimbus for executing SQL.

[kate-goldenring]

@rylev as the sqld-proxy service is written and as Lookup and gluon are implemented, app_id is required for execute. I think in order to add this command, we need to update Lookup in gluon to allow for just project_id and name for a lookup. Then we can run spin cloud sqlite execute "BLAH". Otherwise, it is really hard right now for a user to know what db is associated with what app.

[rylev]

Ok this is ready. We no longer need to send app id so @kate-goldenring's concern above is addressed.