[AIRFLOW-6436] Cleanup for Airflow Configs doc generator code

[kaxil]

Follow Up of #7015 to cleanup code

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Link to JIRA issue: https://issues.apache.org/jira/browse/AIRFLOW-6436

• Description above provides context of the change
• Commit message starts with [AIRFLOW-NNNN], where AIRFLOW-NNNN = JIRA ID*
• Unit tests coverage for changes (not needed for documentation changes)
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions.
• I will engage committers as explained in Contribution Workflow Example.

(*) For document-only changes, no JIRA issue is needed. Commit message starts [AIRFLOW-XXXX].

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In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.
Read the Pull Request Guidelines for more information.

[codecov-io]

Codecov Report

Merging #7036 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #7036      +/-   ##
=========================================
+ Coverage   84.68%   84.7%   +0.02%     
=========================================
  Files         680     679       -1     
  Lines       38686   38647      -39     
=========================================
- Hits        32761   32737      -24     
+ Misses       5925    5910      -15

Impacted Files	Coverage Δ
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	45.25% <0%> (-46.72%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
...rflow/contrib/operators/kubernetes_pod_operator.py	78.75% <0%> (-20%)	⬇️
airflow/hooks/dbapi_hook.py	91.73% <0%> (+0.82%)	⬆️
airflow/models/connection.py	68.78% <0%> (+0.97%)	⬆️
airflow/hooks/hive_hooks.py	77.55% <0%> (+1.53%)	⬆️
airflow/utils/sqlalchemy.py	96.66% <0%> (+6.66%)	⬆️
airflow/operators/mysql_operator.py	100% <0%> (+100%)	⬆️
... and 1 more

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[kaxil]

Preview: https://domineering-growth.surge.sh/configurations-ref.html