Add example of P-chain partial signing #7648

Job	Run time
Fuzz	13m 21s
Unit (macos-12)	14m 39s
Unit (ubuntu-20.04)	6m 54s
Protobuf Lint	5s
Up-to-date protobuf	21s
Unit (ubuntu-22.04)	6m 56s
Up-to-date mocks	1m 54s
Unit (windows-2022)	12m 3s
Unit (custom-arm64-focal)	13m 39s
e2e_existing_network	4m 6s
e2e_post_etna	11m 22s
Unit (custom-arm64-jammy)	12m 2s
e2e_pre_etna	11m 57s
Up-to-date go.mod and go.sum	18s
Lint	3m 21s
Build Antithesis avalanchego images	8m 16s
Build Antithesis xsvm images	11m 50s
Image build	11m 2s
Upgrade	3m 26s
	2h 27m 32s

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