REL4_0_0RC1

This major version of set_user includes the following features:

• Support for PostgreSQL 15
• Previous attempt to support deprecated GUC values surrounding the allowlist/whitelist feature has been removed. The only GUC supported for this now is allowlist. (#56)
• Build with USE_PGXS by default (#69)
• Properly process next object_access_hook (#60)
• Fix server terminated abnormally if executing reset_user() (#58)