Rename `--anat-space-definition` to `--subject-anatomical-reference`

[tsalo]

Closes #847.

Changes proposed in this pull request

• Rename the --anat-space-definition parameter to --subject-anatomical-reference.
  • Rename "first" value to "first-alphabetically".
  • Rename "robust-template" value to "unbiased".
  • Rename "session" value to "sessionwise".
• Mark --longitudinal as a DeprecatedAction.
• Replace uses of longitudinal with subject_anatomical_reference == "unbiased".

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 30.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 28.76%. Comparing base (ee895af) to head (40f0a4b).

Files with missing lines	Patch %	Lines
qsiprep/reports/core.py	0.00%	1 Missing and 2 partials :warning:
qsiprep/cli/parser.py	0.00%	0 Missing and 2 partials :warning:
qsiprep/workflows/anatomical/volume.py	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #855 +/- ## ========================================== - Coverage 28.76% 28.76% -0.01% ========================================== Files 68 68 Lines 10025 10026 +1 Branches 1109 1109 ========================================== Hits 2884 2884 - Misses 7042 7043 +1 Partials 99 99 ```

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