chore(nextcloud): switch to helm-docs

[wrenix]

Description of the change

use helm-docs for documentation

Benefits

No duplicated documentation between README and values.yaml

Possible drawbacks

Not yet so good structed as before, TODOs are:

• [x] give every value in values.yaml a usefull documentation (split to #693 )
• [x] group to sections
• [ ] add extra documentations on the README helm-docs template
• [ ] add ci-job to check if README is uptodate

Applicable issues

fixes #547

Additional information

Readme rendered

Checklist

• [ ] I have read the CONTRIBUTING.md doc.
• [ ] DCO has been signed off on the commit.
• [ ] Chart version bumped in Chart.yaml according to semver.
• [ ] (optional) Parameters are documented in the README.md