docs(user-mgmt): review and revise the `user management` section in the documentation

The [user management](https://docs.jans.io/head/admin/usermgmt/) section needs to be reviewed as it seems to have good amount of overlap with [SCIM configuration](https://docs.jans.io/head/admin/config-guide/scim-config/user-config/) section.

- [Using SCIM](https://docs.jans.io/head/admin/usermgmt/usermgmt-scim/) contains instructions on using CURL to manage users and groups. Should we rename this document or move the content under the [SCIM configuration](https://docs.jans.io/head/admin/config-guide/scim-config/user-config/)
- [Using CLI/TUI](https://docs.jans.io/head/admin/usermgmt/usermgmt-cli-tui/) may have overlap with [SCIM config](https://docs.jans.io/head/admin/config-guide/scim-config/user-config/). And current content in this document is too LDAP centric.
- [Using jans-lik](https://docs.jans.io/head/admin/usermgmt/usermgmt-jans-link/) doesn't have any content. Do we need this document or is it redundant with documents under [Jans Link](https://docs.jans.io/head/admin/link/).

- Instructions in above documents have to be tested as they seem to be dated

Above are some of the thoughts on how to remove redundancy and where updates are required. We can discuss more ideas to make the documentation around user management better.