feat(pageserver): use json for timeline metadata encoding #20978

Job	Run time
check-permissions / check-permissions	1s
tag	11s
cancel-previous-e2e-tests	3s
check-build-tools-image / check-image	6s
build-build-tools-image / check-image / check-image	7s
trigger-custom-extensions-build-and-wait	1m 2s
build-build-tools-image / build-image	0s
build-build-tools-image / merge-images	0s
check-codestyle-rust	16m 6s
check-codestyle-python	31s
build-neon (debug)	10m 21s
compute-node-image (v14)	6m 46s
build-neon (release)	13m 20s
compute-node-image (v15)	7m 9s
neon-image	9m 42s
compute-node-image (v16)	7m 19s
get-benchmarks-durations	0s
vm-compute-node-image (v14)	1m 28s
vm-compute-node-image (v15)	1m 37s
vm-compute-node-image (v16)	1m 36s
test-images	4m 33s
regress-tests (debug, v14)	21m 21s
regress-tests (debug, v15)	21m 11s
regress-tests (debug, v16)	20m 7s
regress-tests (release, v14)	12m 39s
regress-tests (release, v15)	11m 47s
regress-tests (release, v16)	11m 30s
benchmarks	0s
promote-images	1m 51s
trigger-e2e-tests / cancel-previous-e2e-tests	8s
trigger-e2e-tests / tag	11s
trigger-e2e-tests / trigger-e2e-tests	23s
coverage-report (debug)	5m 20s
promote-compatibility-data	0s
deploy	0s
pin-build-tools-image	0s
create-test-report	1m 58s
	3h 10m 24s

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