feat: support https for dex server (#9424)

[notfromstatefarm]

Signed-off-by: notfromstatefarm [email protected]

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Closes #9424

This PR enables HTTPS on the Dex server by sharing the certificate used by argo-server.

[notfromstatefarm]

I'm leaving this as a draft for now. The more I worked on it, the more I thought: should we really be sharing this certificate? When it's self-signed, it's easy peasy TLS setup. But what if someone provides a certificate that matches their domain? It probably won't be valid for the dex server to use.

Going to investigate giving the dex server its own certificate like repo server. Comments appreciated.

[codecov]

Codecov Report

Merging #9881 (b4dfa27) into master (61f321c) will decrease coverage by 0.00%.
The diff coverage is 35.29%.

@@            Coverage Diff             @@
##           master    #9881      +/-   ##
==========================================
- Coverage   45.73%   45.72%   -0.01%     
==========================================
  Files         227      227              
  Lines       26953    26966      +13     
==========================================
+ Hits        12327    12331       +4     
- Misses      12946    12954       +8     
- Partials     1680     1681       +1     

Impacted Files	Coverage Δ
server/server.go	52.83% <0.00%> (-0.35%)	⬇️
util/dex/config.go	84.53% <37.50%> (-4.48%)	⬇️
util/dex/dex.go	88.88% <100.00%> (+1.01%)	⬆️

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[notfromstatefarm]

Closing in favor of a better solution.