core: move P2PNotary node role out of P2PSigExtensions #1121

Job	Run time
Check code generated with 'go generate' is up-to-date	40s
Check internal dependencies	9s
CodeQL (go)	2m 44s
Lint	1m 16s
Coverage	6m 38s
Run tests (ubuntu-22.04, 1.20)	7m 47s
Run tests (ubuntu-22.04, 1.21)	7m 39s
Run tests (windows-2022, 1.22)	19m 22s
Run tests (macos-12, 1.22)	11m 51s
Run tests (macos-14, 1.22)	18m 14s
	1h 16m 20s

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