php8.1 compatibility

Merge pull request #1 from craig-mcmahon/php8-compatability

Improve php8 compatability

1.4

Convert property_type validation from enum to string

Zoopla documentation allows sending any string as property_type as per https://realtime-listings.webservices.zpg.co.uk/docs/latest/documentation.html#appendix_attributes_property_type

1.3

Enable autoload in config