chore: OSS housekeeping round 2

[mayankpande88]

Summary

Second pass of OSS-prep cleanup, addressing items found in a manual review of the repo:

• Delete build_release.sh — leaked Robusta-internal GCP project (us-central1-docker.pkg.dev/genuine-flight-317411/devel/kubewatch) and DockerHub repo (robustadev/kubewatch). Image publishing now lives in .github/workflows/build.yaml targeting GHCR.
• Delete build_with_arm.sh — defunct local-only helper; the workflow handles multi-arch builds via docker buildx.
• Makefile cleanup — replace Travis-era TRAVIS_COMMIT env var (Travis was removed earlier) with GIT_COMMIT. Add VERSION ldflag injection so make build produces a binary that reports its version via kubewatch version, matching what the Docker-built image does.
• Add CODE_OF_CONDUCT.md — reference-only adoption of Contributor Covenant 2.1 with reporting address and pointer to SECURITY.md for vulnerabilities.

Tests performed

• go build ./... clean
• Manually inspected new Makefile by tracing the LDFLAGS expansion: make build VERSION=v0.0.0-test will inject version=v0.0.0-test, gitCommit=$(git describe --tags), buildDate=<now>
• Confirmed no other build scripts reference Robusta infrastructure: grep -rn 'robustadev\|genuine-flight\|robusta-charts' . returns nothing after this PR
• CODE_OF_CONDUCT.md is reference-only and links to the canonical Contributor Covenant text rather than embedding it

Notes for reviewers

CHANGELOG.md was considered but skipped — softprops/action-gh-release already auto-generates per-tag release notes on tag push, making a static CHANGELOG.md duplicate work that goes stale.

go.mod module path stays as github.com/bitnami-labs/kubewatch intentionally — renaming would break anyone consuming the upstream import path. Not critical for OSS release.

[gemini-code-assist]

Code Review

This pull request adds a Code of Conduct, updates the Makefile to support versioning and generic git commit variables, and removes several Docker build scripts. Feedback was provided regarding the Makefile to use the $(shell ...) function for variable assignments instead of backticks to improve robustness and error handling when git is unavailable.