Add brainrender API doc support

[AlgoFoe]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

• To add brainrender API documentation to the BrainGlobe website.

What does this PR do?

• Adds brainrender to the documentation fetch/API generation pipeline and enables its API reference generation.

References

• Issue 96

How has this PR been tested?

• Built the documentation locally and verified the brainrender API pages render correctly.

Is this a breaking change?

• No.

Does this PR require an update to the documentation?

• No.

Checklist:

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