Unify IPPool subnet and ExternalIPPool definitions #32275

Job	Run time
Check whether tests need to be run based on diff	15s
Verify docs and spelling	44s
Unit test (windows-2022)	12m 25s
Go benchmark test	4m 34s
Build Antrea and antctl binaries	9m 47s
Golangci-lint (macos-latest)	5m 51s
Golangci-lint (ubuntu-latest)	9m 50s
Integration test	10m 41s
Unit test (ubuntu-latest)	6m 27s
Build Antrea Windows binaries	1m 50s
Check tidy, code generation and manifest	5m 0s
	1h 7m 24s

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