docs/rfcs: add RFC for fast tenant migration/failover #12900

Job	Run time
check-permissions	1s
tag	18s
check-codestyle-python	28s
check-codestyle-rust	8m 16s
build-neon (debug)	6m 54s
build-neon (release)	6m 23s
compute-tools-image	3m 41s
neon-image	10m 20s
compute-node-image (v14)	17m 18s
trigger-custom-extensions-build-and-wait	2m 50s
compute-node-image (v15)	15m 40s
compute-node-image (v16)	15m 41s
regress-tests (debug, v14)	14m 7s
regress-tests (debug, v15)	11m 0s
regress-tests (debug, v16)	11m 32s
regress-tests (release, v14)	9m 25s
benchmarks	0s
regress-tests (release, v15)	9m 4s
regress-tests (release, v16)	9m 59s
test-images	3m 1s
vm-compute-node-image (v14)	1m 38s
vm-compute-node-image (v15)	1m 26s
vm-compute-node-image (v16)	3m 5s
promote-images	5m 11s
coverage-report (debug)	8m 9s
trigger-e2e-tests	7s
deploy	0s
promote-compatibility-data	0s
create-test-report	4m 3s
	2h 59m 37s

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