Cleanup: Remove container flag (var I)

[gauron99]

Variant I

• This version simply removes the container flag
• Much simpler solution compared to Variant II
• We lose the host builder "defaultability" - you now have to specify --builder=host for all languages to use it.

• Im in favor of this variation as var II introduces some complications which seem unnecessary. This change is simple and can be expanded upon later if desired and doesnt introduce any breaking changes across tests/ CLIs / commands.
• reference: variant II (Cleanup: Remove container flag & make the builder dynamic (var II) #2983)

Changes

• 🧹 Remove the --container flag for func run
• The containerization is determined via builder now in func run

/kind cleanup
Fixes #2973

Release notes

Remove the --container flag - builds are determined via builder itself for func run command

Docs

[knative-prow]

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[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.60%. Comparing base (e4bd40b) to head (3a5dbf3).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/run.go	87.50%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2987      +/-   ##
==========================================
+ Coverage   58.95%   59.60%   +0.64%     
==========================================
  Files         132      132              
  Lines       16944    16919      -25     
==========================================
+ Hits         9990    10085      +95     
+ Misses       6025     5877     -148     
- Partials      929      957      +28     

Flag	Coverage Δ
e2e-tests	41.04% <81.25%> (+1.40%)	⬆️
integration-tests	54.34% <87.50%> (+1.53%)	⬆️
unit-tests	46.53% <87.50%> (+1.09%)	⬆️

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