Please add php7-ldap support

[rwesterflan]

Problem/Motivation

Most applications in my homelab authenticate via LDAP. I can enable it for Bookstack in the envvars, but the module is missing.

Expected behavior

Enable LDAP for logins

Actual behavior

Bookstacks throws an error that PHP-LDAP extension is not installed

Proposed changes

So far, running 'apk add php7-ldap' seems to work, but that's not ideal with updating

[sinclairpaul]

If its just the dependency that's needed, I will add it in the next release.

[rwesterflan]

Thank you very much!