New license request: Add new pretalx AGPL exception

[pombredanne]

License Name
The full name of the license, preferably as provided by the original authors.
TBD

License Homepage URL
The primary and/or most reliable URL that contains the text of this license and/or information about it. This is ideally a web page dedicated to the license, but it may also be a source file that contains the license text.

https://github.com/pretalx/pretalx/blob/main/LICENSES/LicenseRef-Pretalx-AGPL-3.0-Terms.txt

Reference URLs
Optionally provide URLs that contain references to the license.

License Notes
Optionally describe any aspects of the license that deserve special attention.

[pombredanne]

See also pretix exception #4588

[DennisClark]

New license exception LicenseRef-scancode-pretalx-exception-3.0 created in DejaCode enterprise and public. Copyleft.

@AyanSinhaMahapatra please synchronize when you have time, thanks.