Added Alpine 3.15

[xmikus01]

Description

Alpine just released its v3.15 version.

Closes#1610.

Motivation and Context

For more information, see release blog post: https://www.alpinelinux.org/posts/Alpine-3.15.0-released.html

Testing Details

N/A

Example Output(if appropriate)

N/A

Types of changes

• Documentation
• Version change (Update, remove or add more Node.js versions)
• Variant change (Update, remove or add more variants, or versions of variants)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Others (non of above)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• All new and existing tests passed.

[nschonni]

@yosifkit@tianon has this been rolling out to the other official images now? just checking before expanding the CI matrix

[tianon]

Yeah definitely, although we usually drop Alpine 3.13 at the same time in all the repositories we maintain (since Alpine typically has to build from source, so the load of each additional variation is high and thus we limit to "at most two versions supported").

[nschonni]

OK, so the suggestion as a follow up for this would be to drop 3.12 and 3.13 to get it back down to 2. I think we're already at 3 version

[bricss]

Any updates, or ETA when it might land? 🤔

[xmikus01]

@nschonni Rebased and dropped Alpine 3.12 and 3.13 as suggested.

[nschonni]

LGTM!
Think it's better to hold off till after the new years so not to cause any issues over the holidays from the changing default versions

[github-actions]

Created PR on the official-images repo (docker-library/official-images#11605). See https://github.com/docker-library/faq#an-images-source-changed-in-git-now-what if you are wondering when it will be available on the Docker Hub.