Add example app #109

Job	Run time
Lint	18s
Audit	23s
MSRV	1m 49s
Package (rinja)	29s
Package (rinja_actix)	59s
Test (ubuntu-latest, stable)	34s
Package (rinja_axum)	30s
Test (ubuntu-latest, beta)	38s
Package (rinja_derive)	13s
Test (macos-latest, stable)	33s
Test (windows-latest, stable)	1m 21s
Package (rinja_derive_standalone)	40s
Package (rinja_escape)	44s
Package (rinja_parser)	34s
Package (rinja_rocket)	1m 2s
Package (rinja_warp)	33s
Package (testing)	1m 0s
Package (examples/actix-web-app)	52s
	13m 12s

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