Allow configurable range of Job priorities

[alessio-perugini]

#15516

Summary

To allow our users to better fine-grain the job priorities, we're expanding the upper limit from 100 to MaxInt16-1.

• CoreJobPriority is hard-coded to math.MaxInt16 (32767)
• JobMaxPriority defaults to 100 and can be configured in the range 100 <= JobMaxPriority < math.MaxInt16.
• JobDefaultPriority defaults to 50 and can be configured in the range 50 <= JobDefaultPriority < JobMaxPriority
• The new configuration value is set into our server configuration.

Notes for the reviewer

This quick draft aims to gather feedback to understand if the solution is on the right path. After that, I'll add tests, docs, proper commits names, and the other missing stuff.

Bear with me, this is my first time contributing to the codebase. 🙏 I'm looking forward to your comments. 🤓

[hashicorp-cla]

All committers have signed the CLA.

[tgross]

Hi @alessio-perugini! It looks like you've discovered how gross it is to wire up all the configuration so that it makes its way from the agent to the server, and how it gets merged to the default config. So yes, this looks like it's on the right track!

[tgross]

This is looking good, @alessio-perugini!

I've left some comments to address. In addition, if you can run make cl that'll ask you some questions to generate a changelog file for this PR.

[tgross]

I see you picked up the tests, thanks. I think we're getting close on this one

[tgross]

LGTM! I know reviews for seemingly minor features can end up taking a surprising amount of back and of forth. Thanks for sticking with this, @alessio-perugini!

This will ship in Nomad 1.5.0 GA

[alessio-perugini]

@tgross Thank you so much for your patience and help. This was my first time contributing to a project of this scale. I had so much fun working on this. Looking forward to helping you with other issues.
Keep rocking! 🤘