[ENH] - Validate instance types for Google Cloud

[marcelovilla]

Feature description

Right now, we're not validating whether instance types passed in the configuration are valid when initializing the infrastructure. However, we're doing it for AWS and DigitalOcean. See:

• https://github.com/nebari-dev/nebari/blob/aed2b926fc1176fa90e4b23e6ee9dc02ca0e861d/src/_nebari/stages/infrastructure/__init__.py#L517
• https://github.com/nebari-dev/nebari/blob/aed2b926fc1176fa90e4b23e6ee9dc02ca0e861d/src/_nebari/stages/infrastructure/__init__.py#L282

Value and/or benefit

Besides being consistent with what we have with other providers, it would enhance the user's experience when specifying unavailable/non-existing instance types before running into an error halfway through the deployment.

Anything else?

No response

[marcelovilla]

@blakerosenthal since you're interested in this issue, here are a couple pointers that you might find useful:

• We'll likely need to implement the instances function in the following file: https://github.com/nebari-dev/nebari/blob/379736eb365ca5f7c5da769d578df5961bb644c2/src/_nebari/provider/cloud/google_cloud.py
• We recently merged a PR (see: https://github.com/nebari-dev/nebari/pull/2083). In that PR we switched from using subprocess + gcloud to using the Google Python APIs. We used to have an instances function but it was not being used anywhere so we got rid of it and opened this issue to make sure we'd implement it using the Google Python APIs in the future.