Doc: Protobuffer vesion

[jdsika]

OSI Documentation still mentions protobuf > 3.0.0

[ClemensLinnhoff]

And that should be changed to >= 2.6.1?

[jdsika]

@pmai do we have a decision here from the CCB?

[pmai]

CCB 2024-05-13: Fix with PR that changes the two references in doc/setup/installing_prerequisites.adoc to 2.6.1. @pmai to create PR and merge today.