fix(docs): sort sources by display name in doc's sidebar

[Masterchen09]

This PR fixes the order of the sources in the sidebar of the documentation: Previously the sources were automatically sorted by the name of the corresponding markdown file resp. the platform id (the files are named by the platform id). The fix ensures that the corresponding sidebar_position metadata attribute is added to the generated markdown files after the sources were sorted by the platform name (the attribute is needed for the autogenerated sidebar here).

This fixes/reverts #7244 by renaming the SAP HANA source to "SAP HANA" instead of "HANA". I have also seen that the Apache NiFi source was called "Nifi" instead of "NiFi" (see here), therefore I have also quickly renamed it to "NiFi" in this PR.

@RainerGa FYI

edit: I have also renamed the generic SQLAlchemy source to "SQLAlchemy" instead of "Other SQLAlchemy databases", because when sorting the sidebar by the platform name, the source is not sorted after "S" anymore (additionally the long title look ugly in the sidebar):

vs.

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub