Add `libstd-go` package

**What I'd like:**

Currently, Bottlerocket does not have a clear way to report Go advisories from CVEs patched in the `bottlerocket-sdk` repository.

One solution is to add a no-op `libstd-go` package to the core-kit that we tag Go vulnerabilities to, which would simplify the BRSAs for them.

**Any alternatives you've considered:**

N/A

Start by tracing how package definitions are added in core-kit and how Go CVEs from the bottlerocket-sdk repository are represented in BRSAs. Done means a no-op libstd-go package exists in core-kit and can be used to tag the relevant Go advisories.

Written by the indexing model from the issue text.