Introduces a required issue template for requesting the inclusion of new PostgreSQL extensions into the containers project.

This template ensures all necessary information is provided upfront, specifically requiring:

• Confirmation that no duplicate request exists.
• Project metadata (name, URLs, description, license).
• Mandatory confirmation that the license is compliant.
• Identification of known dependent extensions.
• Explicit commitment from the proposer to act as the Component Owner and maintain the extension image in compliance with project governance.

Closes #41