ci: add support for custom GOPROXY and GOSUMDB in Docker environment

[lokielse]

Description

This PR adds support for passing custom GOPROXY and GOSUMDB environment variables to the Docker-based build environment. This enhancement enables developers working in enterprise environments with restricted network access or corporate proxies to successfully run builds and validation commands.

Changes Made

• Modified build/makefile/golang.mk to conditionally pass GOPROXY and GOSUMDB environment variables to Docker containers when they are set in the host environment
• Updated .gitignore to exclude vendor/ directory and /generate-dep.go file

Problem Solved

Developers in enterprise environments often encounter certificate verification errors when running make validate or other build commands due to corporate network restrictions. For example:

level=error msg="Running error: context loading failed: failed to load packages: failed to load packages: failed to load with go/packages: err: exit status 1: stderr: go: downloading go1.24.4 (linux/arm64)\ngo: download go1.24.4: golang.org/[email protected]: verifying module: golang.org/[email protected]: Get \"https://proxy.golang.org/sumdb/sum.golang.org/supported\": tls: failed to verify certificate: x509: certificate signed by unknown authority\n"

With this change, developers can now set custom proxy configurations:

GOPROXY=https://corporate.proxy.com/go GOSUMDB=off make validate

Related Issues

Fixes #

Checklist

Note: Ensure your PR title follows the Conventional Commits format (e.g., feat(scheduler): add new feature)

• Self-reviewed
• Added/updated tests (if needed)
• Updated CHANGELOG.md (if needed)
• Updated documentation (if needed)

Breaking Changes

None. This change is backward compatible - if GOPROXY and GOSUMDB are not set, the build process behaves exactly as before.

Additional Notes

• The implementation uses ifneq conditionals to only pass these environment variables when they are explicitly set, maintaining backward compatibility
• This is particularly useful for developers behind corporate firewalls or in regions with restricted access to public Go proxy servers
• Common use cases include setting GOSUMDB=off to disable checksum verification or using GOPROXY=https://proxy.golang.org,direct for alternative proxy configurations