Properly cast type

The current logic is checking whether:

1. The returned value is a boolen
2. The returned value is a string and then matches for "true"

Since the config is now written to the database the data is now a string with the value "1" if HTTPS is set to true. Effectively this option was thus always disabled at the moment, falling back to plain HTTP.

This change casts the data to a boolean if it is defined as boolean.

Fixes https://github.com/owncloud/core/issues/22605
Fixes https://github.com/owncloud/core/issues/22016