chore: add MPL-2.0 license for public release

[devin-ai-integration]

Summary

Adds the Mozilla Public License 2.0 (LICENSE file) in preparation for making the repository and GHCR packages public.

MPL-2.0 is a file-level copyleft license — modifications to existing files must remain open, but the operator can be combined with proprietary code in a Larger Work without imposing license obligations on the surrounding project. This is a good fit for infrastructure tooling that others may embed in their own deployment pipelines.

Post-merge steps (manual)

After merging this PR:

1. Make the repo public: Settings → General → Danger Zone → Change repository visibility → Public
2. Make the container package public: Navigate to https://github.com/orgs/bcit-tlu/packages → haproxy-operator → Package settings → Danger Zone → Change package visibility → Public
3. Make the Helm chart package public (if published separately): Same as above for the charts package

Review & Testing Checklist for Human

• Verify the LICENSE text matches the canonical MPL-2.0 from mozilla.org
• Confirm MPL-2.0 aligns with BCIT institutional open-source policy

Notes

No code changes — license file only. CI will run go-test and helm-lint as usual; both are unaffected.

Link to Devin session: https://app.devin.ai/sessions/4e8b458306c24377a7b5485185b9d30f
Requested by: @kphunter

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.