Disallow editing environment name

What does this MR do?

When the user changes the environment name, slug and tire aren't updated, which leads to bugs like #31268 (closed).

And we can't update slug with the name as it's used by AutoDevOps jobs in k8s namespace names. If we update it, subsequent deployment jobs can fail/deploy to new namespace.

We can go back to random slug, but it requires reverting some chanks of 36a01a88 which is super complex. Also, it allow users to create environment "Test" with the slug "production-random-suffix" which would be very counter-intuitive.

So this MR just disables the name field in the UI. See more arguments for this: #31268 (comment 653655448).

Users can always just remove the old environment and create a new one with the same name.

Screenshots

Before After
Screenshot_2021-08-24_at_14.06.41 Screenshot_2021-08-25_at_18.50.39

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Related to #31268 (closed)

Edited by Andrew Fontaine