[precheck] False-positives: Provide option to use HTTP GET instead of defaulted HTTP HEAD (CDNs block) #30163

As a developer I'd like to have option to set HTTP Method to GET instead of HEAD for precheck_metadata so that I don't need to allow HTTP HEAD via my CDN configurations.

To reproduce:

1. URL in metadata that will block HTTP HEAD with 403

Observed

1. False positive from:

| privacy URL: (ms) | HTTP 403: https://site.com |

Expected

1. provide http_check_method=GET for precheck
2. 200 OK