Update alpine and pwsh versions

What does this MR do?

As per our latest policy updates !3931 (diffs)

• This MR updates the alpine versions we support to ones that still have support as per https://endoflife.date/alpine.
• With this MR we will support alpine 3.15, 3.16 and 3.17. Before we used to support alpine 3.12, 3.13, 3.14 and 3.15.
• The default images such as docker pull gitlab/gitlab-runner-helper:x86_64-latest will now point to alpine 3.17 as opposed to alpine 3.15 which was the case before. My thinking is that we can change the default image to point to the latest alpine on every major release since it will have support year on year so our default images will never be without support.
• These changes have the added bonus that all these alpine versions now support a powershell variant, while before we only had up to 3.13.
• In order to support all of these alpine versions alongside powershell I had to update powershell to 7.3, which I think is a good time to do in a major release. There's lts-7.2, however it does not support all the alpine versions sadly.

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The process of updating these wasn't smooth so improvements could be made for next year 🤔

Why was this MR needed?

To align with our policy and get rid of old versions and use new ones.

What's the best way to test this MR?

What are the relevant issue numbers?

Closes #29639 (closed)