docs: update kratos doc

[agathanatasha]

This PR updates the kratos helm chart install documentation. The doc is updated with a complete kratos-config.yaml where users could install kratos without errors. I also updated the section on setting identity schemas, providing up to date options. I removed the --set-file option from identity schema section as I can't reproduce it.

Related Issue or Design Document

#449

Checklist

• [x] I have read the contributing guidelines and signed the CLA.
• [x] I have referenced an issue containing the design document if my change introduces a new feature.
• [x] I have read the security policy.
• [x] I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security vulnerability, I confirm that I got green light (please contact [email protected]) from the maintainers to push the changes.
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added necessary documentation within the code base (if appropriate).

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