www/ilias: Update version 7.16=>8.0b2

• Flavorize the port for different php versions
• Remove pecl-pdf dependency as it is no longer marked as dependency in the upstream documentation

Although upstream mentioned about releasing version 8 before the expiry
of php74 unfortunately the schedule has been delayed and will take place
some times next year. So rather the reaping the port I am considering to
update to a beta release which supports php 8.0.

PR: 261610
Approved by: portmgr (blanket infrastructure)
Sponsored by: Bounce Experts