chore: upgrade eslint backend to 9.0

[TCMeldrum]

Part of UserOfficeProject/issue-tracker#1488

Description

Our eslint version is end of life and out of support: https://eslint.org/version-support/ so I have updated the backend to 9.0.0 and will open new prs for the frontend and tests to avoid the prs form getting too big. 9.0.0 comes with a new config format so I have migreated to that however this has come with some rule updated and changes. I have tryed to keep the rules as consistant as before but in some cases it doesnt seem possible right now e.g. import-js/eslint-plugin-import#2721. I have also updated the code base to follow some new (or previously missing? idk) rules that seem sensible to follow.

I suggest reviewing this PR commit by commit to see the rule updates applyed one at a time and not all at once.

Motivation and Context

Eslint v8 is end of life and out of support

How Has This Been Tested

Created new eslint.config.js for v9, updated to code base to follow updated rules.

Fixes

Changes

Depends on

Tests included/Docs Updated?

• I have added tests to cover my changes.
• All relevant doc has been updated

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[github-actions]

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[jekabs-karklins]

question/suggestion: I see this cleans up nicely many places when it comes to formatting, at the same time I wonder if we could be less oppinionated on the import order. A lot of times it causes unneeded conflicts and I rarely do I find it helpful if imports are alphbetical with linespaces withing the group. Do you feel the same way and if so is there a way to downprioritize the import rules

[TCMeldrum]

I haven't felt that it is too opressive my code editor is very good at correcting it with one click, I also quite like the seperation of the external npm modules and relivite imports. I think it also nice to be able to see which module is being imported when we have some classes with the same name e.g. Fap and Fap.

That being said I am not wedded to it, happy to be over ruled.