RPM spec: modernize Python to 3.x for RHEL

[space88man]

Is your feature request related to a problem? Please describe.
Since CentOS(7) is dropped as a target, update Python to 3.x in spec file for easier packaging.

Building on EL8+ distros should use Python 3.x; since RHEL8 is at plateau phase and the last (& final) Python version is 3.12, target that version - which also works on EL9/CentOS Stream 10

Describe the solution you'd like
Update RPM spec to Python 3 (preferably Python 3.12, the last and final version for EL8)

Describe alternatives you've considered
Maintain out-of-tree freeswitch.spec for packaging on RHEL8, RHEL9, CentOS Stream 10
Example: EL8-spec-out-of-tree

It is painful to maintain this out-of-tree

Additional context
n/a

Package version or git hash

• Version of FreeSWITCH - 1.10.12