Restrict E2E and starter templates to supported regions

[paulbatum]

Purpose

Set the allowed locations for flex consumption deployment, so that AZD prompts the user with valid options. Uses the same @allowed as from the IaC sample.

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

Run azd up for a new environment for any of the E2E samples and confirm that the location list is appropriately filtered

[nzthiago]

Thank you!