CLOUDP-296898: use errors for termination

[s-urbaniak]

For dry-run we need to be able to notify about errors during dry-run reconciliation. These can be various failure modes like:

• Atlas API not reachable (5xx)
• Connection secrets not being configured correctly
• internal errors

Currently, there is no way to distinguish reconcile results from failure results. This fixes it by adding errors vs. strings to our Terminate* methods. Dry-run is going to read out this error, skip on the the internal dry-run errors, and report everything else as an event.

Note: this is also a good intermediate for future optimisation of error return handling in conjunction with idiomatic controller-runtime error handling.

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[github-actions]

https://app.codecov.io/github/mongodb/mongodb-atlas-kubernetes/commit/18af694370e3d41c127d191d633d4744dc287c00

[josvazg]

👌