'Resolves an endpoint for a service and region combination.
:type service_name: string
:param service_name: Name of the service to resolve an endpoint for
(e.g., s3)
:type region_name: string
:param region_name: Region/endpoint name to resolve (e.g., us-east-1)
if no region is provided, the first found partition-wide endpoint
will be used if available.
:rtype: dict
:return: Returns a dict containing the following keys:
- partition: (string, required) Resolved partition name
- endpointName: (string, required) Resolved endpoint name
- hostname: (string, required) Hostname to use for this endpoint
- sslCommonName: (string) sslCommonName to use for this endpoint.
- credentialScope: (dict) Signature version 4 credential scope
- region: (string) region name override when signing.
- service: (string) service name override when signing.
- signatureVersions: (list<string>) A list of possible signature
versions, including s3, v4, v2, and s3v4
- protocols: (list<string>) A list of supported protocols
(e.g., http, https)
- ...: Other keys may be included as well based on the metadata'

def construct_endpoint(self, service_name, region_name=None):

    raise NotImplementedError
