Add option to specify dynatrace.conf.yaml as part of prepare project

[robertjahn]

In order to support custom tags for Dynatrace events, one must pass in dynatrace.conf.yaml.

Solution is to add an addition input field to the extension. The default form value is blank. Here is a mockup

Reference: https://github.com/keptn-contrib/dynatrace-service#sending-events-to-dynatrace-monitored-entities

[heydenb]

Fixed since 1.0.4