Support grpc-php-rs

[Wouter0100]

Since the normal grpc extension has various issues with FrankenPHP, we recently switched to grpc-php-rs. The maintainer is very helpful and fixed one (rather stupid, but imho not his fault's) "bug" we've had, but thus far has been really stable.

Way easier and less heavy to compile as well. Would be very nice to have it supported by the extension installer.

[mlocati]

Since grpc-php-rs is not available on pecl, and it doesn't provide a package.xml file, it's not compatible with install-php-extensions

[Wouter0100]

Thanks, @mlocati for your quick response. I've opened an issue at grpc-php-rs and will get back to you.