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

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #31268 (closed)