Read MLEM metafiles with description and labels

[aguschin]

We deprecated them a while but were able to read them still, but not so long ago a change in MLEM made these files unreadable. Some repos still have those, such as https://github.com/iterative/demo-bank-customer-churn, which is needed to be read in Studio now.

Besides, I'm switching try_migrations=True to automatically try to read and fix old metafile formats. @mike0sv, you initially set it to False - did you have any specific concerns in mind for that?

cc @amritghimire @jellebouwman - once this is merged and released we need to check if the MLEM models in the repo can be read without any troubles. I'll ask your help with that @amritghimire

[codecov]

Codecov Report

Patch coverage: 93.33% and project coverage change: +1.67 🎉

Comparison is base (c08038a) 84.41% compared to head (e84744e) 86.09%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #630      +/-   ##
==========================================
+ Coverage   84.41%   86.09%   +1.67%     
==========================================
  Files         107      107              
  Lines        9716     9728      +12     
==========================================
+ Hits         8202     8375     +173     
+ Misses       1514     1353     -161     

Impacted Files	Coverage Δ
mlem/core/metadata.py	97.97% <ø> (ø)
mlem/api/migrations.py	94.73% <88.88%> (-1.19%)	⬇️
mlem/core/objects.py	87.33% <100.00%> (+0.06%)	⬆️
mlem/api/utils.py	78.18% <0.00%> (+5.45%)	⬆️
mlem/api/commands.py	89.72% <0.00%> (+5.47%)	⬆️
mlem/contrib/docker/utils.py	83.49% <0.00%> (+24.27%)	⬆️
mlem/contrib/docker/base.py	85.00% <0.00%> (+27.81%)	⬆️
mlem/contrib/rabbitmq.py	98.76% <0.00%> (+45.67%)	⬆️

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