Add logic to fallback to global endpoint if region detection through environment variable and imds fails.

[neha-bhargava]

In case MSAL fails to detect the region, fallback to global endpoint.

Please refer to the design doc for details.

Currently we will only fallback to global when region detection fails and not when regional ests fail. For regional ests failures we are waiting on the ests-r team to provide us with the allow list of errors for which we need to fallback to global.

• Add an api FallbackToGlobal in the confidential client WithAzureRegion(AutoDetectRegion: true, FallbackToGlobal: true)
• Fallback logic in case we fail to detect the region -- first request decides this and then cache
• Add to telemetry if we are falling back to global for the request

[bgavrilMS]

@neha-bhargava @trwalke - isn't this done?

[pmaytak]

This is included in MSAL 4.25.0 release.