Added workspace mount point as option to build

[jkutner]

Summary

Allow the workspace directory to be configurable.

Output

Before

$ pack build ...

After

$ pack build --workspace app ...

Documentation

• Should this change be documented?
  • Yes, see #___
  • No

Related

Resolves #1121

[codecov]

Codecov Report

Merging #1141 (21a7929) into main (4d4f310) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1141      +/-   ##
==========================================
+ Coverage   80.77%   80.80%   +0.03%     
==========================================
  Files         136      136              
  Lines        8289     8299      +10     
==========================================
+ Hits         6695     6705      +10     
  Misses       1164     1164              
  Partials      430      430              

Flag	Coverage Δ
os_linux	80.29% <100.00%> (+0.08%)	⬆️
os_macos	77.82% <100.00%> (+0.07%)	⬆️
os_windows	80.71% <100.00%> (+0.03%)	⬆️
unit	80.29% <100.00%> (+0.03%)	⬆️

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[dwillist]

@jkutner Hey thanks for the PR, any chance we could get some associated testing here at whatever level you're comfortable with? Codecov seems a little suspect 🤨

[jkutner]

@dwillist done

[dfreilich]

This is great! Happy to see this driven out, given the recent feedback on it. If you could just change the assertions in the test a bit to more accurately test the change, that would be 🤯