[feature] move installer generation to CI

[duncdrum]

the signed installers should be generated on CI only, and removed from the default build profiles

see #3394

[adamretter]

@duncdrum That would break the ability to build a release of eXist-db.

[duncdrum]

@adamretter how so? In effect, it would allow more people to act as release manager, without necessitating signing certs on the local machine.

By making/keeping installers profiles opt-in will reduce complexity within our org, and for new contributors. No more !dmg-on-mac flags for simple compiles.

Doing custom builds of installers will work by using the profile. In the rare cases that folks want to do so.