Track tables as "read-only" (don't provide mutations)

### Is your proposal related to a problem?

I don't always want to provide insert/update/delete mutations for the tables I track and expose through hasura. Yes I know permissions can be used down the line to "hide" the mutations. I just don't want them in the first place.

### Describe the solution you'd like

In the "GRAPHQL FEATURES" section at the bottom of the "Modify" page of a given table, I want a checkbox / toggle that says "Set table as Read Only" or something similar.

The Custom GraphQL Root Fields section should NOT offer custom Mutation names either.

### Describe alternatives you've considered

I prefix all my mutations with something like DO_NOT_USE_xxx and eventually hide them through permissions.