Reduce list to only the available ones for gpt-4o-mini/Standard

[pamelafox]

Purpose

As pointed out by @Jbrocket on PR #2443, I did not change the regions list to only the ones that support gpt-4o-mini/text-embedding-ada002 with Standard sku, the current default models. That means that a new developer may pick a region like canadaeast which has no support for the model.

This PR changes the allowed list to the regions for gpt-4o-mini, Standard. Unfortunately, this means that existing developers who used other regions will get an error from Bicep, due to their region not being on the allowed list. They will have to manually add it when they see the error.

I talked with the azd team about this, and I only see one good solution to have less region issues: default to GlobalStandard, which has a consistent set of region support. However, to do that, we need to migrate text-embedding models, as ada-002 effectively is not in GlobalStandard. So that's a larger change.

Also, we'd need to message clearly the change to GlobalStandard, since that may not be permissible for some customers, like those in Europe.

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[X] Yes - For existing developers.
[ ] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by this tutorial
which includes deployment, settings and usage instructions. If text or screenshot need to change in the tutorial,
check the box below and notify the tutorial author. A Microsoft employee can do this for you if you're an external contributor.

[ ] Yes
[X] No

Type of change

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

Code quality checklist

See CONTRIBUTING.md for more details.

N/A