Added links to amplify docs on existing ts docs

[yuhengshs]

Description of changes

Added links to link Amplify JS apis to their respective API docs page on the ts doc string.

Issue #, if available

Description of how you validated changes

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

Checklist for repo maintainers

• Verify E2E tests for existing workflows are working as expected or add E2E tests for newly added workflows
• New source file paths included in this PR have been added to CODEOWNERS, if appropriate

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.