feat: Add the necessary scaffolding for a dark mode theme

[tete17]

Signed-off-by: tete17 miguel_tete17@hotmail.com
#4722

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• Optional. My organization is added to USERS.md.
• I've signed the CLA and my build is green (troubleshooting builds).

Technically this PR doesn't add any new features. It simply adds the necessary scaffolding for the Ui to implement a future dark mode.

I initially intended to submit a complete PR with the complete feature but after discovering the existence of https://github.com/argoproj/argo-ui I realised I would need to make a PR there too. My intention now is to submit this short one first to get some experience on how things run in the argo world and then submit progressive PR to fully implement the dark mode.

I also want to open this soon to know if this is something the argo team really wants, is not something spent the effort or has a specific implementation plan in mind.

I also attach a small gif with the user experience

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #4929 (94c0724) into master (345c77a) will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4929      +/-   ##
==========================================
- Coverage   41.44%   41.35%   -0.10%     
==========================================
  Files         128      128              
  Lines       17666    17666              
==========================================
- Hits         7322     7305      -17     
- Misses       9292     9313      +21     
+ Partials     1052     1048       -4     

Impacted Files	Coverage Δ
controller/appcontroller.go	50.56% <0.00%> (-1.92%)	⬇️

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[rbreeze]

Are you planning on implementing the completed dark mode feature yourself?

Would you consider opening this PR for another branch (i.e. one called dark-mode? It's unlikely this PR will get merged to master since it's an incomplete feature. Using a separate branch would be more conducive to how you want to develop this.