Idea for CodeChecker toolchain

[furtib]

Why:
We want to use toolchains to determine which CodeChecker binary to use.

What:

• Created a toolchain for CodeChecker following the Bazel documentation (https://bazel.build/extending/toolchains)
• Make per_file rule use the toolchain (not the monolithic, since that does not use use_default_shell_env)

Addresses:
none?

Notes:

• Looking around in other toolchains: rules_go and rules_python it seems toolchains are usually under a folder named the program - in out case CodeChecker (python for rules_python, go for rules_go) - this seems to be to have the toolchain path be //codechecker:toolchain_type instead of //src:toolchain_type.
• For the local toolchain in the future, I would want to use the path collected in tools.bzl