Draft: NetpuneLogger checkpoint saving reworked

[Raalsky]

What does this PR do?

• NeptuneLogger will upload model checkpoints for best-K checkpoints without already uploaded ones -> Less data will be sent to Neptune server
• Best K models will be resilient to local file deletions
• Best model will not be duplicated and reuploaded

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📚 Documentation preview 📚: https://pytorch-lightning--19144.org.readthedocs.build/en/19144/

[codecov]

Codecov Report

Merging #19144 (bf11a96) into master (df869c9) will decrease coverage by 34%.
Report is 2 commits behind head on master.
The diff coverage is 93%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19144      +/-   ##
==========================================
- Coverage      83%      49%     -34%     
==========================================
  Files         443      435       -8     
  Lines       36764    36609     -155     
==========================================
- Hits        30617    17971   -12646     
- Misses       6147    18638   +12491     

[Borda]

let's update or rebase after #19265 lands 🎏

[gitguardian]

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[Borda]

@Raalsky is it still a draft?