docs: use absolute links and update link targets #3288

Job	Run time
prepare-binaries	4s
buildkit-edge	1m 19s
prepare-test-integration	1m 27s
test-unit (ubuntu-22.04)	43s
test-unit (macos-12)	1m 9s
test-unit (windows-2022)	2m 30s
binaries (darwin/amd64)	1m 25s
binaries (darwin/arm64)	1m 23s
binaries (linux/amd64)	1m 25s
binaries (linux/arm/v6)	1m 34s
binaries (linux/arm/v7)	1m 24s
binaries (linux/arm64)	1m 33s
binaries (linux/ppc64le)	1m 30s
binaries (linux/riscv64)	1m 24s
binaries (linux/s390x)	1m 19s
binaries (windows/amd64)	1m 22s
binaries (windows/arm64)	1m 31s
test-integration (docker, ./tests)	4m 24s
test-integration (docker\+containerd, ./tests)	4m 12s
test-integration (docker-container, ./tests)	3m 3s
test-integration (remote, ./tests)	2m 55s
release	11s
bin-image	0s
	37m 47s

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