Don't call for storageConnetionString if it's not needed

[nturinski]

Fixes #4900

For creating flex + managed identity, storageConnectionString is never used but still computed. That's the unnecessary call that triggers the error since it's not available with storage accounts that have SAS turned off.

Also have a fallback for storage endpoint suffix, but it was previously hard-coded before, so it probably didn't work for other clouds.

[Copilot]

Pull request overview

This PR avoids unnecessarily fetching the storage connection string when creating a Flex function app with managed identity, which previously caused errors for storage accounts with SAS disabled. It also replaces hard-coded core.windows.net storage endpoint suffixes with environment-aware values for multi-cloud support.

Changes:

• Skip fetching storageConnectionString when creating a Flex app with managed identity, since only service URIs are used in that scenario.
• Extract a getStorageEndpointSuffix helper that reads the storage endpoint suffix from the Azure environment (with fallback), replacing hard-coded core.windows.net.
• Use nonNullProp as a runtime assertion on storageConnectionString at all usage sites to fail fast if it's unexpectedly undefined.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/utils/managedIdentityUtils.ts	Added getStorageEndpointSuffix helper and replaced hard-coded core.windows.net in blob/queue/table service URIs with the environment-aware suffix.
src/commands/createFunctionApp/FunctionAppCreateStep.ts	Conditionally fetches storageConnectionString only when needed; moved plan-type boolean declarations earlier; wrapped usages in nonNullProp assertions.