chore: prepare for open source

[rabelloo]

As instructed in https://www.notion.so/primerio/Open-sourcing-Repositories-64ea9a537b604d7e83965c34ce44b6f3

• Attach an appropriate license
  • get approval from Alex
  • select a license which limits liability, and if necessary maintains copyright
  • guideline: https://www.notion.so/primerio/Licensing-404a5f02551144e5a0d9818f8b74c303
• Create a Contribution Guide
  • ask POps to validate it (N/A)
• Populate .gitignore with sensitive file patterns
  • .env / .env.example (sanitised)
  • *.pem / .crt
• Company-email configured for authorship (no personal emails)