Fixed issues that were present in v1.4 for PostgreSQL 18.

Adding support for PostgreSQL 18. Also, updating the pg_background

What's Changed

• Enhanced Compatibility: Validated and tested the code with PostgreSQL 17 to ensure compatibility and stability.
• Simplified Privilege Management: Introduced new functions (grant_pg_background_privileges and revoke_pg_background_privileges) to streamline the process of granting and revoking privileges for the pg_background extension.
• Improved Documentation: Updated the README file to reflect the latest changes, acknowledge contributors, and provide clear licensing details.
• Enhanced Error Handling: Improved error reporting by displaying exception and error messages in the client's preferred encoding (contributed by @joelhecht).

What's Changed

• add PGDLLEXPORT to pg_background_work_main for pg16 by @a-mckinley in #48

New Contributors

• @a-mckinley made their first contribution in #48

Full Changelog: v1.1...v1.2

• Added support for PostgreSQL 15. (@rjuju )

This is the first version for of pg_background which has support for PostgreSQL >= 9.5