Add BGP confederation support in BGPPolicy #35219

Job	Run time
Check whether tests need to be run based on diff	21s
Verify docs and spelling	54s
Unit test (windows-2022)	13m 19s
Unit test (ubuntu-latest)	7m 53s
Integration test	6m 23s
Golangci-lint (ubuntu-latest)	9m 36s
Go benchmark test	5m 13s
Build Antrea and antctl binaries	13m 26s
Golangci-lint (macos-latest)	7m 36s
Check tidy, code generation and manifest	4m 20s
Build Antrea Windows binaries	2m 20s
	1h 11m 21s

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