go-sdk is missing functionality to fetch SLI configs

[christian-kreuzberger-dtx]

Several integrations for fetching SLIs use a function called GetSLIConfiguration which is part of go-utils:
https://github.com/keptn/go-utils/blob/65503489d75aac53e74e089babc7a5258887d93c/pkg/lib/keptn/keptn_base.go#L83-L86

This function requires a KeptnBase instance to be present, which in return requires a cloud event to be present (among other things like KeptnOptions), e.g.:

// gotEvent processes an incoming CloudEvent
func gotEvent(event cloudevents.Event) error {
	keptnHandler, err := keptnv2.NewKeptn(&event, keptncommon.KeptnOpts{})

	customQueries, err := keptnHandler.GetSLIConfiguration(project, stage, service, utils.SliResourceURI)
	if err != nil {
		return nil, err
	}
...

By switching to the go-sdk approach for implementing handlers, we are losing this functionality, as

• It seems that it's not possible to get a "KeptnBase" object out of the sdk,
• It's not a good idea to use NewKeptn, as we're lacking the actual Cloud Event as well as keptn options (also, reconstructing the cloud event seems to be not the best idea... - but feel free to proof me wrong).

Problem

The lack of this implementation within go-sdk means that all services that are currently using GetSLIConfiguration need to re-implement this functionality based on the sdk. A first approach has already been done by dynatrace-service:
https://github.com/keptn-contrib/dynatrace-service/blob/ddfadcff9a656974fe4e0d81c54c94602de3fce8/internal/keptn/config_client.go#L136-L172
(this also has context.Context as params, which is helpful)

This means that we will have multiple different implementations of this function, which will lead to increased maintenance costs for everyone involved in the future.

In addition, the GetSLIConfiguration will most likely no longer be-usable in go-utils, therefore we will have dead-code in go-utils.

Evidence of Usage

• prometheus-service
• sumologic-service https://github.com/keptn-sandbox/sumologic-service/blob/54cf849cb74d89444d49e4e288dd1219716214df/eventhandlers.go#L157
• datadog-service https://github.com/keptn-sandbox/datadog-service/blob/6d7cf1883b8b194c9d4894708c1b7977f4f05495/eventhandlers.go#L84

Proposal (please discuss)

• Provide an easier way to use GetSLIConfiguration when using go-sdk

[warber]

I agree that this should not be implemented over and over again, but rather refactored/extracted into its own helper function that can be accessed independently of KeptnBase as a first step. KeptnBase in turn should be deprecated.

[arthurpitman]

The main motivation for the implementation in the dynatrace-service linked above was to add a context.Context to be used when accessing the underlying resources. Furthermore, once the dynatrace-service switched to using the controlplane connector, we no longer really needed to use KeptnBase.

[christian-kreuzberger-dtx]

@arthurpitman @warber I'd suggest that the new implementation also has a context.Context parameter, and uses the new SDK functions for fetching files.

Edit: Would it be possible to move https://github.com/keptn-contrib/dynatrace-service/blob/ddfadcff9a656974fe4e0d81c54c94602de3fce8/internal/keptn/config_client.go#L128-L172 into go-sdk?