Custom build gosu with current go to remove CVEs

[nathanlaceyraft]

Summary

gosu security policy https://github.com/tianon/gosu/blob/master/SECURITY.md says they don't update golang for CVE's
So gosu is build with a unsupported version of go (1.20)

The two support go versions that have the most CVE's resolved are 1.23.6 and 1.24.0
I felt using 1.23.6 was a safer upgrade.

This PR custom builds gosu with a currently supported go version.
And copies it into the final image.

trivy image --scanners vuln wiremock/wiremock:3.12.0
shows that we'll get rid of the following CVE's

usr/local/bin/gosu (gobinary)

Total: 58 (UNKNOWN: 0, LOW: 1, MEDIUM: 23, HIGH: 31, CRITICAL: 3)

Thanks for your consideration

References

#129

[mguezuraga]

Hi, bumping this! We have several CVEs marked here because this was built using 1.18.2