[Docs] fix docstring and documentation used for hub.get_model

[zengyh1900]

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Motivation

MMdetection has renamed some configs https://github.com/open-mmlab/mmdetection/tree/3.x/configs
The docstring and documentation used in mmengine.hub.get_model should be updated.

Modification

'faster_rcnn' -> 'faster-rcnn'

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Base: 78.40% // Head: 78.40% // No change to project coverage 👍

Coverage data is based on head (05b20d1) compared to base (3aba989).
Patch has no changes to coverable lines.

❗ Current head 05b20d1 differs from pull request most recent head 0f798b0. Consider uploading reports for the commit 0f798b0 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #659   +/-   ##
=======================================
  Coverage   78.40%   78.40%           
=======================================
  Files         127      127           
  Lines        9175     9175           
  Branches     1826     1826           
=======================================
  Hits         7194     7194           
  Misses       1670     1670           
  Partials      311      311           

Flag	Coverage Δ
unittests	78.40% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmengine/config/utils.py	58.49% <ø> (ø)
mmengine/hub/hub.py	25.71% <ø> (ø)

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