Remove hardcoded default SLI definitions

[arthurpitman]

Current situation
Right now the dynatrace-service always offers default SLIs even if none are derived from a dashboard or specified in the associated sli.yaml.

Describe the solution you'd like
When services are onboarded or monitoring is configured for a project, a default sli.yaml is created together with a default dynatrace.conf.yaml via the configuration service, making the configuration completely clear to the user at any given point in time (via the project's git repository)

[j-poecher]

Since dynatrace-service has reached EOL on December 22nd, 2023, this issue has been closed.