[docs-only] Create envvar delta files after v5 to master (v7.0.0)

[mmattel]

This PR:

• Adds a Python script generating the delta files automatically based on configuration. Note that we can compare any version that has been tagged or branched including master after v6! This means we do not need to wait until releasing has been done.
• Adds added/removed/deprecated adoc files for the admin docs. This is very important to finalize the upgrade/migration guide

Note that the respective .md files can only be created AFTER releasing as this requires (currently) a semver version to be accessed which mster is not.

I will file a second PR with some necessary doc helper stuff.

NOTE: To make this PR work, else hugo wants to render adoc files but has no parser configured, we needed to adapt config.yaml from hugo at its source to exclude directories: owncloud/owncloud.github.io#94

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud