Standardize modular documentation

[SkafteNicki]

📚 Documentation

Similar to the work done in this PR:
#1360

We want to standardize the way documentation is organised for modular metrics. This includes:

• update and compute are excluded from docs as the docstrings are often not meaningful to begin with. Instead information about input/output tensors should be included in the class docstring
• references are moved to the links.rst file
• Sections are organised as
  • Introduction to metric
  • Input/output format
  • Args
  • Raises
  • examples
• shape information is formatted as ``(N, d)`` (normal brackets and double ticks)
• math if formatted using the :math: directive

Some of the points also apply to the functional backend, but the modular backend is of most importance because it has the largest variance in how information is organised currently.

Following domains needs to be taken care of

• Aggregation -> Improve docs on aggregation #1369
• Audio -> Update audio docs #1360
• Classification -> Return info / formatting on Classification docs #1433
• Image -> Update image docs #1407
• Detection -> Update docs on Detection metrics #1372
• Regression -> Update regression docs #1410
• Retrieval -> Add output / format input info to retrieval docs #1429
• Text -> Update text docs #1416

Any contributions are welcome :]

[theja-vanka]

Hi, Please assign Detection task to me. A bit of grooming will be helpful to deliver asap.

[reaganjlee]

All the docs should have been addressed now, let me know if there's anything else