chore(deps): bump github.com/spf13/viper from 1.19.0 to 1.20.0-alpha.6

[lvlcn-t]

Motivation

The new viper pre-release removes the cumbersome feature flag from the build process. Instead we can apply a new option to apply the feature flag on runtime: spf13/viper#1706 (comment) spf13/viper#1854

Relates to #78
Closes #172

Changes

I've removed the feature flag from our goreleaser configs and am now using the viper option.

For additional information look at the commits.

Tests done

Works locally with setting the gitlab token for the target manager per environment variable:

{"time":"2024-06-10T12:53:04.362093156+02:00","level":"INFO","source":{"function":"github.com/caas-team/sparrow/cmd.NewCmdRun.run.func1","file":"/home/installadm/dev/github/sparrow/cmd/run.go","line":89},"msg":"Running sparrow"}
{"time":"2024-06-10T12:53:04.36232596+02:00","level":"INFO","source":{"function":"github.com/caas-team/sparrow/pkg/sparrow/targets.(*manager).Reconcile","file":"/home/installadm/dev/github/sparrow/pkg/sparrow/targets/manager.go","line":82},"msg":"Starting target manager reconciliation"}
{"time":"2024-06-10T12:53:04.36241834+02:00","level":"INFO","source":{"function":"github.com/caas-team/sparrow/pkg/config.(*FileLoader).Run","file":"/home/installadm/dev/github/sparrow/pkg/config/file.go","line":71},"msg":"File Loader disabled"}
{"time":"2024-06-10T12:53:04.362358777+02:00","level":"INFO","source":{"function":"github.com/caas-team/sparrow/pkg/api.(*api).Run.func1","file":"/home/installadm/dev/github/sparrow/pkg/api/api.go","line":101},"msg":"Serving Api","addr":":8080"}
{"time":"2024-06-10T12:54:04.854148679+02:00","level":"INFO","source":{"function":"github.com/caas-team/sparrow/pkg/sparrow/targets/remote/gitlab.(*client).FetchFiles","file":"/home/installadm/dev/github/sparrow/pkg/sparrow/targets/remote/gitlab/gitlab.go","line":88},"msg":"Successfully fetched all target files","files":2}

• Unit tests succeeded
• E2E tests succeeded - we have none for this

TODO

• I've assigned this PR to myself
• I've labeled this PR correctly