feat: add --import-map option

[kt3k]

This PR adds --import-map option. You can run the command with custom import map path.

deno run -A jsr:@deno/bump-workspaces/cli --import-map ./import_map.json

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.

Project coverage is 80.95%. Comparing base (f21af28) to head (1df6a76).

Files	Patch %	Lines
mod.ts	69.23%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
- Coverage   81.39%   80.95%   -0.45%     
==========================================
  Files           2        2              
  Lines         559      567       +8     
  Branches       79       80       +1     
==========================================
+ Hits          455      459       +4     
- Misses        103      107       +4     
  Partials        1        1              

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[kt3k]

tested in denoland/std#5824