gconfig.py should not use python3 but gwms-python

[mmascher]

Describe the bug Some sites do not have python3 and the gconfig.poy fails when it is executed as a validation script since it has python3 in the shebang.

Expected behavior We should use the gwms-python wrapper for the shebang so that the script works on all sites

Screenshots

Executing (flags:) /data/glide_1anBib/main/gconfig.py
/usr/bin/env: python3: No such file or directory
=== Validation error in /data/glide_1anBib/main/gconfig.py ===
Wed Sep 13 17:10:37 CEST 2023 Error running '/data/glide_1anBib/main/gconfig.py'
     The test script did not produce an XML file. No further information available.
Wed Sep 13 17:10:37 CEST 2023 Notifying VO of error
Removed condor variables
Advertising failure to the VO collector

Info (please complete the following information):

• GlideinWMS version: 3.10.3
• Priority: high
• Stakeholders: FactoryOps
• Components: glidein