Initial Pattern fork of grate

chore: rename module path to github.com/patterninc/grate (#2)

Rename the Go module from github.com/pbnjay/grate to
github.com/patterninc/grate (go.mod + all internal import paths) so the
Pattern-owned fork can be imported directly without a replace directive.

Co-authored-by: Shivang Nagta <shivang.nagta@SGNAGTA-PAT-IN.local>