Role to configure nextcloud with LDAP User backend.

First test passed.

New modules:

- occ:
  set coniguration values using `php occ` nextcloud command-line tool.

Created a reusable tasks list for issung certificates (tls) at the
moment.

Added option for module cert_request to programmatically require
signing of client certificate.

Stripping newlines from TLS request Certificate Signing Request cause
ca_manager to fail.

We have to check if SSH cert request are still working.

Add support for OpenSSH v8 (ouput of `ssh-keygen` changed slightly) in
module `ssh_cert` and use a better implementation for multiple user CA.

Now we are reading user_ca from `group_vars/all.yaml`.
`user_ca_keys` should be list of each allowed User CA on one host (in
this way is easier to rotate CAs without reissuing keys to each user at
the same time).
The production CA must be the first one in the list. Host certificate
will be checked only against the first CA and updated if their host key
was issued from another CA in the list.

For this reason now we are using a template to create
`/etc/ssh/user_ca.pub` on the target, to preserve the key order.

`group_vars/all.yaml.example` has been updated to reflect the new usage.

Mainly string vs bytes-string issues.

Compatibility with Python 2.x now broken.

this module will help parsing the result of ssh certificates
and certification authorities to validate them