Unify documentation links stable versus version number

[wollmers]

Some links use version number like

https://doc.otobo.org/doc/manual/config-reference/10.0/en/content/core.html#fqdn

others use stable like

https://doc.otobo.org/manual/admin/stable/en/content/users-groups-roles/agents-groups.html

[wollmers]

See also RotherOSS/otobo#585

[wollmers]

This issue needs coordination across all repositories, websites and tool chains.

[wollmers]

Proposed URL scheme similar to other popular software packages like MySql, Apache, PostgreSQL:

https://doc.otobo.org/manual/<DOCUMENT>/<VERSION>/<LANGUAGE>/<PATH_TO_PAGE>

Examples:

https://doc.otobo.org/manual/admin/stable/en/content/users-groups-roles/agents-groups.html
https://doc.otobo.org/manual/admin/10.0/en/content/users-groups-roles/agents-groups.html
https://doc.otobo.org/manual/admin/devel/en/content/users-groups-roles/agents-groups.html

where stable and devel are aliases to an URL using a version number.