describe architecture of the lifecycle-operator

[StackScribe]

Part of https://github.com/keptn/lifecycle-toolkit/issues/770

Expand the architectural information in https://lifecycle.keptn.sh/docs/concepts/architecture/components/lifecycle-operator/ .

• Some source material in https://github.com/keptn/lifecycle-toolkit#readme . Note that this material was written before we separated the metrics-operator from the lifecycle-operator and other modifications so some material may need to be updated
• Study the source code for the lifecycle-operator to verify the information and possibly add new information.
• Study logs generated by the lifecycle-operator to see if they give insights and ensure that the documentation provides info the user needs to follow the logs.

[github-actions[bot]]

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