Add cargo cache to github actions

[clangenb]

Can be done exactly the same way as in:

https://github.com/integritee-network/parachain/blob/c8b642f02bc6aeb1bf183aa211227fd9c20f75a3/.github/workflows/build.yml#L25

[brenzi]

I suggest to copy-paste the entire CI/CD flow of the parachain repo