docs: Fixed typos in API jsdoc

[brnhensley]

Just some typo corrections and clarifying custom attributes are added to the active Span as well as the Transaction

Description

Please provide a brief description of the changes introduced in this pull request.
What problem does it solve? What is the context of this change?

How to Test

Please describe how you have tested these changes. Have you run the code against an example application?
What steps did you take to ensure that the changes are working correctly?

Related Issues

Please include any related issues or pull requests in this section, using the format Closes #<issue number> or Fixes #<issue number> if applicable.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}