Added MongoDB example #4400

Job	Run time
check-docs	27s
cargo-hack	3m 15s
check	45s
cargo-public-api-crates (axum)	36s
cargo-public-api-crates (axum-core)	29s
cargo-deny check (advisories)	53s
dependencies-are-sorted	14s
cargo-public-api-crates (axum-extra)	30s
Spell Check with Typos	5s
cargo-deny check (bans licenses sources)	23s
cargo-public-api-crates (axum-macros)	19s
test-msrv	2m 19s
armv5te-unknown-linux-musleabi	20s
test-docs	1m 34s
test-nightly	1m 32s
test-versions (stable)	1m 29s
test-versions (beta)	1m 29s
wasm32-unknown-unknown	13s
	16m 52s

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