Harmonize output paths of `morphometrics` commands

[FrancescoCasalegno]

Description

The output of the morphoclass morphometrics sub-commands extract-features and train now have the same file naming convention of morphoclass extract-features and morphoclass train.

Example for extract-features:

# output of `morphometrics exctract-features`
dvc/extract-features-morphometrics/in-L1/all/features.csv

# output of `exctract-features` (for `diagram-deepwalk`)
dvc/extract-features/in-L1/all/diagram-deepwalk/*.features

Example for train:

# output of `morphometrics train`
dvc/training/checkpoints-morphometrics/in-L1-all-morphometrics-xgb-stratified-k-fold/checkpoint.chk

# output of `train` (for `diagram-deepwalk` with `perslay`)
dvc/training/checkpoints/in-L1-axon-diagram-deepwalk-perslay-stratified-k-fold/checkpoint.chk

Checklist

• [x] This PR refers to an issue from the issue tracker. (if it is not the case, please create an issue first).
• [x] All CI tests pass.