CI | RPM Github Actions | Refactor RPM actions & Create nightly RPM builds on stage_5.15.4 branch

[romayalon]

Explain the changes

1. Add a nightly build for stage_5.15.4 branch - this action should be temporary.
2. Changed the structure of the current RPM github actions to the following structure -

• RPM build base (workflow_call)
• Upload to aws (workflow_call)
• RPM build and upload flow (workflow_call & a caller - calls RPM build base and upload to aws, 2 different calls, one per each centos version)
• Manual build (caller, calls to RPM build base)
• Nightly master build - (caller - calls RPM build and upload flow, master branch)
• Nightly stage_5.15.4 build - (caller - calls RPM build and upload flow, stage_5.15.4 branch)

Issues: Fixed #xxx / Gap #xxx

Testing Instructions:

• Doc added/updated
• Tests added