Invalid info what to put into "provider" field for Group LDAP Links

[gdubicki]

Info provided in https://github.com/egnyte/gitlabform/commit/06f158d78bdc5ce0f79956906e19e179242f4bda is invalid.

This should be a value that I don't yet know where to get from GitLab config or with API but in the UI it is shown here:

- it's "ldapmain" in this example.