[Chronik] Install Rust platform targets required for CI

Summary: To run the builds on all the supported OS's and CPUs, we need to add the platform targets via rustup.

Test Plan:

1. docker run -i -t bitcoinabc/bitcoin-abc-dev
2. Run the commands added in this diff -> adds the platform targets
3. source $HOME/.cargo/env
4. cargo new --bin hello && cd hello
5. cargo build --target x86_64-pc-windows-gnu
6. file target/x86_64-pc-windows-gnu/debug/hello.exe -> outputs something like PE32+ executable (console) x86-64, for MS Windows

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11865