docs: Add fully-local developer workflow and traps

[AndiDog]

I found that only the virtualized toolchain with make start is explained, but working locally is a lot faster (webpack rebuilds, Go rebuilds take seconds instead of minutes on macOS x64). Therefore I wrote down a step-by-step guide how to get a whole Kubernetes + Argo CD development environment working locally, including any potential errors and their workarounds.

• 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).
• [n/a] I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• [n/a] 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.
• [n/a] Optional. My organization is added to USERS.md.
• I have signed off all my commits as required by DCO
• [n/a] I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• [n/a] My build is green (troubleshooting builds).

[codecov]

Codecov Report

Merging #10333 (5cd0317) into master (6756a5f) will decrease coverage by 0.20%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10333      +/-   ##
==========================================
- Coverage   46.13%   45.92%   -0.21%     
==========================================
  Files         228      229       +1     
  Lines       27961    28278     +317     
==========================================
+ Hits        12900    12987      +87     
- Misses      13315    13518     +203     
- Partials     1746     1773      +27     

Impacted Files	Coverage Δ
util/cert/cert.go	75.57% <0.00%> (-6.25%)	⬇️
server/logout/logout.go	77.77% <0.00%> (-6.10%)	⬇️
server/application/application.go	28.30% <0.00%> (-3.82%)	⬇️
util/io/files/tar.go	52.99% <0.00%> (-3.58%)	⬇️
reposerver/repository/repository.go	61.95% <0.00%> (-2.39%)	⬇️
util/gpg/gpg.go	64.65% <0.00%> (-2.31%)	⬇️
cmd/argocd/commands/app.go	18.91% <0.00%> (-0.62%)	⬇️
pkg/apis/application/v1alpha1/repository_types.go	68.60% <0.00%> (-0.54%)	⬇️
util/settings/settings.go	51.36% <0.00%> (ø)
controller/appcontroller.go	52.31% <0.00%> (ø)
... and 10 more

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[crenshaw-dev]

This is awesome!

Can you change "ArgoCD" to "Argo CD"? Either way is fine, but in docs we've tended to go with the latter. :-)

[AndiDog]

Can you change "ArgoCD" to "Argo CD"? Either way is fine, but in docs we've tended to go with the latter. :-)

Left it consistent on purpose, but I like that spelling even more. Changed in a new commit, since I replaced it in the whole file.

[crenshaw-dev]

Thanks so much @AndiDog!