Reorganise contributing guide into multiple pages

[niksirbi]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other: restructuring docs

Why is this PR needed?

See #808, part of the larger #704 effort.

What does this PR do?

• Splits contributing guide into separate pages
• Expands on "Before you start" section
• Massively expands our testing guide (which was non-existent other than benchmarks)
• Adds a maintainer guide
• Corrects a few other places throughout

References

Closes #808.

How has this PR been tested?

Local docs build. I recommend reviewing it in the same way.

Is this a breaking change?

Only in the sense that the previous link to the contributing guide (https://movement.neuroinformatics.dev/latest/community/contributing.html) will no longer work.

We'll henceforth have links to specific pages, e.g. https://movement.neuroinformatics.dev/latest/community/implementing-loaders.html

When wanting to reference contribution guidelines as a whole, the community index works fine.

Does this PR require an update to the documentation?

It is an update of docs.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (447492e) to head (2bedb21).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #826   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           36        36           
  Lines         2205      2205           
=========================================
  Hits          2205      2205           

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[niksirbi]

Would be nice to include here some instructions on merging/rebasing when PRs get out-of-sync.

We could include @sfmig's favourite resources:

• See here for a nice explanation on rebasing
• See here for a bit more details on merging conflicts and force push

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud