added documentation for get_standard_gate_name_mapping (backport #13230)

[mergify]

Summary

Added documentation for the function get_standard_gate_name_mapping() in the Standard Gates section here.
#Closes #13108

Details and comments

I have added the necessary details about the function with code examples in the documentation.

---

This is an automatic backport of pull request #13230 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 3889fe0 has failed:

On branch mergify/bp/stable/1.2/pr-13230
Your branch is up to date with 'origin/stable/1.2'.

You are currently cherry-picking commit 3889fe0bf.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   qiskit/circuit/library/standard_gates/__init__.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   qiskit/circuit/library/__init__.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[qiskit-bot]

Thank you for opening a new pull request.

Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient.

While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone.

One or more of the following people are relevant to this code:

• @Cryoris
• @Qiskit/terra-core
• @ajavadia

[mtreinish]

I'm going to close this because we're about to release 1.3.0rc1 and this isn't necessary on the stable/1.2 anymore.

[1ucian0]

ooppss.. I thought it will hit stable/1.3. Done in #13230 (comment)

EDIT: the bot is smart enough to realize that it was not needed. Good bot 🤖 (beep boop)