Add SRU exception for Valkey

[lvoytek]

This PR will require approval from an SRU team member

I will also update the [TBD] sections if an SRU team member approves :)

Description

Add an SRU exception for the Valkey package to speed up future updates to stable releases. Prior to this, Valkey has gone through the standard SRU process for version updates 4 times:

LP: #2127122
LP: #2097546
LP: #2091129
LP: #2115258

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Checklist

• I have read and followed the Ubuntu Project contributing guide
• I have tested my changes, and they work as expected

[basak]

Thank you for preparing this! I think this sounds fine in principle. I had a couple of questions which I think are mostly addressed by https://valkey.io/topics/releases/ that you linked, but maybe it's worth making this more explicit in this (our) documentation?

• Upstream have strict documented rules for maintaining compatibility in their micro updates
• This special case documentation covers only micro updates, not minor or major updates

Given what happened with bind9, did we say we'd do the following in all cases or just that one? I think we said we'd do it generally, right?

• Whoever prepares the SRU will check over the upstream release notes of reported upstream changes we're taking to ensure that all upstream changes match our expectations of what a micro release is, confirm that in the bug they've done that, and call out anything that seems like it might be close to the line.

I think you're planning on doing this all anyway but reading the text I'm not sure it's explicit. Could you make this explicit, please?

Upstream testing seems comprehensive and the autopkgtests are there. I think all the criteria in https://documentation.ubuntu.com/project/SRU/reference/requirements/#reference-criteria-microreleases are therefore met, so this side all seems good.

This isn't a +1 yet - I'd like confirmation from other SRU team members that they're happy with my review - but if we could make the above more explicit in the docs please, I think this will be good to go.

[lvoytek]

Thanks Robie! Added the new standard section on avoiding breaking changes and noted the todos in the template and step by step process.

Currently I'm happy with the special case just covering micro releases, since minor releases very often have breaking changes, such as 8.1 no longer being compatible with Redis while 8.0 mostly was

[lvoytek]

Also added note on why minor releases are not considered