Insert the role in `auth.roles` when a new role is added to the Hasura metadata

[plmercereau]

@nunopato we have to make sure the Postgresql user that Hasura Auth uses to connect is authorized to add an event trigger on the hdb_catalog schema.

See this discussion

Closes #103

[elitan]

I would probably not implement this in Hasura Auth and instead push the responsibility to the developer to manage manaually for now.

[szilarddoro]

I'm closing this PR because it's stale.