[clang-tools-extra] [clang-tidy][docs] Rename static analyzer check docs to Markdown (PR #211448)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `clang-tools-extra` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/61018

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang Tools :: clang-tidy/infrastructure/update-checks-list.test' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/usr/bin/python3.10 /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_update_docs.py -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/update-checks-list.test.tmp.clang-tidy-checks-list.rst
# executed command: /usr/bin/python3.10 /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_update_docs.py -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/update-checks-list.test.tmp.clang-tidy-checks-list.rst
# .---command stderr------------
# | Traceback (most recent call last):
# |   File "/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_update_docs.py", line 93, in <module>
# |     sys.exit(main(sys.argv[1:]))
# |   File "/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_update_docs.py", line 80, in main
# |     generated = generate_updated_list()
# |   File "/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_update_docs.py", line 57, in generate_updated_list
# |     subprocess.run(
# |   File "/usr/lib/python3.10/subprocess.py", line 526, in run
# |     raise CalledProcessError(retcode, process.args,
# | subprocess.CalledProcessError: Command '['/usr/bin/python3.10', '/tmp/lit-tmp-5nm33gu9/tmpudbih0zy/clang-tools-extra/clang-tidy/add_new_check.py', '--update-docs']' returned non-zero exit status 1.
# `-----------------------------
# error: command failed with exit status: 1

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/211448