Upgrade Command: Source the proxy address from env var

[steiler]

implementing #2505

[steiler]

@toweber can you try this out, please?

[toweber]

Looks good from my end now

[hellt]

thanks!

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 52.20%. Comparing base (b789b6a) to head (5e36308).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/version/upgrade.go	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2507      +/-   ##
==========================================
- Coverage   52.22%   52.20%   -0.03%     
==========================================
  Files         173      173              
  Lines       17862    17869       +7     
==========================================
  Hits         9328     9328              
- Misses       7546     7553       +7     
  Partials      988      988              

Files with missing lines	Coverage Δ
cmd/version/upgrade.go	4.44% <0.00%> (-0.82%)	⬇️

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.