Support Release Channel in Bundle Resolution

[fabiocav]

Description

The Azure Functions host needs to consider the platform's release channel when resolving extension bundles. The release channel will be provided through the environment variable WEBSITE_PlatformReleaseChannel. This improvement ensures bundle resolution aligns with platform expectations.

Release Channel Definitions

The WEBSITE_PlatformReleaseChannel environment variable will have the following possible values:

• Latest: Behaves as it does today. Resolves to the latest available version of the bundle that meets the customer’s specified reference.
• Standard: Resolves to the version prior to the latest (n-1), if that version is available.
• Extended: Resolves to the version two releases prior to the latest (n-2), if that version is available.
  • However, Functions and Rapid Update should treat Standard and Extended the same, resolving to n-1.

Expected Behavior

• When resolving bundles, the host should check the value of WEBSITE_PlatformReleaseChannel and apply the corresponding versioning logic.
• If the variable is not set, default to Latest behavior.