[master] Add primary_extension attribute to extension_metadata
This is used from DIRAC 7.3 onwards to decide which extension is the "main" one that is running (e.g. what does the version passed into the system administrator refer to).
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This is used from DIRAC 7.3 onwards to decide which extension is the "main" one that is running (e.g. what does the version passed into the system administrator refer to).