Web console should not allow schema changes when running *.cli-migrations images

### Is your proposal related to a problem?
I recently switched over to using the `hasura/graphql-engine:v2.0.9.cli-migrations-v3` image and explicit migrations/metadata tracking for the config-as-code and reproducibility benefits when working across dev/prod/staging, etc.

Everything was working great, and I was able to make schema changes in the web console and have those recorded automatically in my `migrations/` directory by virtue of using the console through `hasura console` instead of `HASURA_GRAPHQL_ENABLE_CONSOLE=true`.

Fast forward to an accidental configuration change earlier this week: inadvertently, I now had `HASURA_GRAPHQL_ENABLE_CONSOLE=true` and accessed the console directly instead of via `hasura console`. As a result, all schema changes since then have not been persisted. So now I have significant drift between what's recorded in `migrations/` and the actual hasura schema.

This is a huge footgun.

See https://hasura.io/docs/latest/graphql/core/migrations/migrations-setup.html#step-0-disable-the-console-on-the-server for more info.

### Describe the solution you'd like
Either,
1. Using `*.cli-migrations` images implies `HASURA_GRAPHQL_ENABLE_CONSOLE: "false"`
2. Allow the web console, but disallow the user from making any schema changes in that mode. Instead provide an error message directing them to run via `hasura console`.

### Describe alternatives you've considered
n/a

### If the feature is approved, would you be willing to submit a PR?
Sure, if someone can point me to where the changes would be required.