fix: Hf callback metric naming

[MikhailKardash]

Ticket

https://hpe-aiatscale.atlassian.net/browse/MD-511

Description

TRAIN = "train_progress" appears to be a confusing variable name for a value that is intended as a placeholder. This caused an issue in the behavior of on_log(). This PR renames TRAIN to DEFAULT and TRAIN_PROGRESS to TRAIN

Test Plan

Run an example with huggingface callback and make sure metrics are being recorded properly.

Checklist

• Changes have been manually QA'd
• New features have been approved by the corresponding PM
• User-facing API changes have the "User-facing API Change" label
• Release notes have been added as a separate file under docs/release-notes/
  See Release Note for details.
• Licenses have been included for new code which was copied and/or modified from any external code

[netlify]

✅ Deploy Preview for determined-ui canceled.

Name	Link
🔨 Latest commit	6d010a3
🔍 Latest deploy log	https://app.netlify.com/sites/determined-ui/deploys/66d25c5fa11bbb0008c1191c

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.43%. Comparing base (d54713c) to head (6d010a3).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9887      +/-   ##
==========================================
- Coverage   54.69%   50.43%   -4.27%     
==========================================
  Files        1261     1106     -155     
  Lines      156700   144542   -12158     
  Branches     3597     3597              
==========================================
- Hits        85708    72898   -12810     
- Misses      70861    71513     +652     
  Partials      131      131              

Flag	Coverage Δ
harness	49.46% <ø> (-23.16%)	⬇️
web	54.45% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

see 245 files with indirect coverage changes