Provide docker image for cargo-contract

Created by: atenjin

For substrate runtime, parity uses srtool(https://github.com/paritytech/srtool) to compile wasm. And Solang as well, providing a docker image which contrains newest Solang. (https://github.com/hyperledger-labs/solang/blob/main/Dockerfile)

And we think cargo-contract could also provide such docker image. This docker image could resolve the following things:

1. The wasm compilation target for same ink contract may be different in different computer, that is way substrate runtime needs srtool to generate deterministic result.
2. For windows, many users do not have cmake by default, thus, windows users need to parpare cmake before install. If using docker, windows users do not need to install cmake.
3. For our 3-rd parties, like RedSpot(https://redspot.patract.io/), if we want to unify different environment, an existed docker image is a good choice.

Thus, we help cargo-contract provides a docker image by default.