docs: explain about the conditional default metadataBase on vercel de… #27908

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Job	Run time
Determine changes	8s
validate-docs-links	14s
build-native / build	23s
build-next / build	25s
test unit	0s
types and precompiled	0s
test cargo unit	0s
rust check	0s
rustdoc check	0s
test turbopack dev	0s
test turbopack development integration	0s
test turbopack production	0s
Test new tests for flakes (dev)	0s
test next-swc wasi	0s
test next-swc wasm	0s
test turbopack production integration	0s
test dev	0s
Test new tests for flakes (prod)	0s
test prod	0s
test firefox and safari	0s
test integration	0s
test ppr integration	0s
test ppr dev	0s
test ppr prod	0s
lint / build	1m 39s
report test results to datadog	0s
thank you, next	1s
	2m 50s

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