Restructure how method signatures are documented

[watson]

Currently API method signatures are documented in several different ways throughout the agent documentation. We should go over it and align them all in a common format.

[bmorelli25]

This is a duplicate of #925, which was closed in the following PRs:

• docs: add info about when API's were added docs: add info about when API's were added #1000
• docs: fix 'added in' for span API docs docs: fix 'added in' for span API docs #1397
• [docs] Standardize API reference [docs] Standardize API reference #975