Add walk-timeout command line flag

[smaye81]

Adds a walk-timeout flag to certain commands that involve walking the directory structure.

If no walk-timeout is specified where applicable, 3 seconds (3s) will be used as the default which is the current default. Therefore, this maintains backwards compatibility with current walk timeout and allows users to override at a command-level.

Fixes #516

[codecov]

Codecov Report

Merging #545 into dev will increase coverage by 0.16%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##              dev     #545      +/-   ##
==========================================
+ Coverage   66.09%   66.26%   +0.16%     
==========================================
  Files         144      144              
  Lines        7462     7490      +28     
==========================================
+ Hits         4932     4963      +31     
+ Misses       2023     2019       -4     
- Partials      507      508       +1     

Impacted Files	Coverage Δ
internal/file/file.go	100.00% <ø> (+10.00%)	⬆️
internal/cmd/templates.go	84.08% <90.90%> (+0.48%)	⬆️
internal/cmd/flags.go	100.00% <100.00%> (ø)
internal/exec/exec.go	73.52% <100.00%> (+2.56%)	⬆️
internal/exec/runner.go	53.25% <100.00%> (+0.05%)	⬆️
internal/file/proto_set_provider.go	69.94% <100.00%> (+1.03%)	⬆️

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[smallsamantha]

niiice