Remove xcp_d_dir and clean datasinks

[tsalo]

Closes none.

Changes proposed in this pull request

• Drop config.execution.xcp_d_dir in favor of the existing config.execution.output_dir.
• Rename any figure-generating datasinks to start with ds_report_ and drop datatype="figures".
• Loop over nodes and automatically set datatype to "figures" for nodes starting with ds_report_.
• Loop over nodes and automatically set base_directory to config.execution.output_dir for nodes starting with ds_.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.40%. Comparing base (4fd16f1) to head (a232926).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1262      +/-   ##
==========================================
- Coverage   78.47%   78.40%   -0.07%     
==========================================
  Files          59       59              
  Lines        7218     7204      -14     
  Branches     1064     1064              
==========================================
- Hits         5664     5648      -16     
- Misses       1284     1286       +2     
  Partials      270      270              

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