Add approaches for `sum-of-multiples` exercise #2366

Job	Run time
markdown lint	7s
configlet lint	4s
Clippy	8s
Check compilation (stable)	9s
Check exercises on nightly (benchmark enabled)	13s
Check compilation (beta)	15s
Check Rust Formatting	26s
Run shellcheck on scripts	4s
Run repository tests	36s
	2m 2s

Provide feedback