R-106240 makes the HVol VES being a *must*, which is not true.

Proposed text:

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Requirement: R-106240
target: PNF
keyword: MUSTSHOULD
introduced: casablanca
update: El Alto
The following VES Events MUST SHOULD be supported by the PNF: pnfRegistration VES Event, HVol VES Event, and Fault VES Event. These are onboarded via he SDC Design Studio.

Note: these VES Events are emitted from the PNF to support PNF Plug and Play, High Volume Measurements, and Fault events respectively.

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