feat: init PgElection with candidate registration #21773

Job	Run time
Build GreptimeDB binaries (ubuntu-20.04)	3m 29s
Build GreptimeDB binary (profile-CI) (ubuntu-20.04)	3m 41s
Check (windows-2022)	3m 39s
Check typos and docs	6s
Clippy	3m 54s
Check (ubuntu-20.04)	2m 34s
coverage	0s
Rustfmt	49s
Check License Header	2m 10s
Toml Check	28s
Sqlness Test (Basic)	4s
Fuzz Test (fuzz_create_table)	2s
Sqlness Test (Remote WAL)	15s
Fuzz Test (fuzz_alter_table)	16s
Fuzz Test (fuzz_create_database)	2s
Fuzz Test (fuzz_create_logical_table)	2s
Fuzz Test (fuzz_alter_logical_table)	2s
Fuzz Test (fuzz_insert)	2s
Fuzz Test (fuzz_insert_logical_table)	15s
Fuzz Test (Distributed, ${{ matrix.mode.name }}, ${{ matrix.target }})	1s
Fuzz Test with Chaos (Distributed, ${{ matrix.mode.name }}, ${{ matrix.target }})	1s
Unstable Fuzz Test	1s
	21m 53s

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