cache migrate: add utility for migrating local cache files to 3.x

[pmrowla]

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Thank you for the contribution - we'll try to review it as soon as possible. 🙏

related: #4658

requires iterative/dvc-data#389

Adds dvc cache migrate to move local cache files into 3.x cache location and then link the 2.x location -> 3.x location

[pmrowla]

asciinema recording is too big to be uploaded to the asciinema site, the gif conversion is a bit off but should be close enough

[codecov]

Codecov Report

Patch coverage: 37.03% and project coverage change: -0.05 ⚠️

Comparison is base (5c1487e) 90.55% compared to head (40c0a69) 90.51%.

❗ Current head 40c0a69 differs from pull request most recent head 536b6a8. Consider uploading reports for the commit 536b6a8 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9591      +/-   ##
==========================================
- Coverage   90.55%   90.51%   -0.05%     
==========================================
  Files         470      470              
  Lines       35939    35964      +25     
  Branches     5180     5183       +3     
==========================================
+ Hits        32545    32553       +8     
- Misses       2800     2817      +17     
  Partials      594      594              

Impacted Files	Coverage Δ
dvc/cachemgr.py	73.68% <12.50%> (-16.48%)	⬇️
dvc/commands/cache.py	88.23% <72.72%> (-4.45%)	⬇️

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