feat: improved error on remote deploy without local source

[lkingland]

Give a more informative error when attempting to run a func deploy --remote --git-url=x that we still need local source.

This is needed because, conceptually local source would not be required for this case, but we need to update the remote build pipeline flow to check out the code on-demand in order for it to read metadata (like function name). For now, this code flow expects the source code to be available locally.

/kind enhancement

[knative-prow]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 62.53%. Comparing base (1cccfd3) to head (5b18733).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/deploy.go	0.00%	10 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2885      +/-   ##
==========================================
+ Coverage   57.96%   62.53%   +4.56%     
==========================================
  Files         129      129              
  Lines       15767    15851      +84     
==========================================
+ Hits         9140     9912     +772     
+ Misses       5785     4996     -789     
- Partials      842      943     +101     

Flag	Coverage Δ
e2e-tests	43.06% <0.00%> (+7.87%)	⬆️
integration-tests	48.73% <0.00%> (?)
unit-tests	48.85% <0.00%> (-0.27%)	⬇️

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