Roll back Alpine floating tags from 3.22 to 3.21

[lbussell]

This PR moves the Alpine floating tags from 3.22 to 3.21 due to this issue with OpenSSL 3.5 and CosmosDB:

• aspnet:8.0-alpine - OpenSSL 3.5.0 appears to cause frequent connection failures with Azure CosmosDB SDK running in Direct connection mode #6560
• Direct mode connections fail frequently when linked against OpenSSL >= 3.5.0 [Alpine Linux 3.22] Azure/azure-cosmos-dotnet-v3#5302

Related:

• Alpine 3.22 images now available #6488
• Alpine Floating Tags Updated to Alpine 3.22 #6536

[richlander]

We are reverting this change because there is a significant incompatibility between Azure CosmosDB and OpenSSL 3.5. The team needs more time to investigate and respond. OpenSSL 3.5 is the biggest OpenSSL release since OpenSSL 3.0. Alpine 3.22 is the first distro version to include it that we publish in our container images.

The alpine floating time is a convenience service we offer users. We do the following:

• Update the floating tag to reference the newest Alpine version one month after it ships.
• We wait for a month to ensure that there are no known issues with the new release, generally, or with .NET in particular.
• We have delayed updating the floating tag based on known issues multiple times in the past.
• If we learn that there are issues after changing the floating tag, we will revert that change.

In short, users rely on this tag precicely because we'll move it foward and backward based on signal.

We offer fixed version tags for users that want more certainy.

Examples (of both styles):

• 8.0-alpine
• 8.0-alpine3.21
• 8.0-alpine3.22