Remove 'DisableMergedConfiguration' FeatureFlag used in AzureStorageProvider

Introduced a FeatureFlag to disable the merged configuration approach in AzureStorageProvider to use both WebHost and JobHost configurations.

Adding this issue to eventually remove this when this hotfix is stable and performing as expected.

Locate the DisableMergedConfiguration feature flag and its use in AzureStorageProvider, then read the surrounding configuration and flag-handling code. Confirm that the hotfix is stable as described in the issue before removing the flag and its obsolete path; done means AzureStorageProvider uses the merged configuration approach without the disable switch.

Written by the indexing model from the issue text.