[BUG] Docker distributions don't set API failures as `rejected` in redux

[ohltyler]

Certain redux store variables, relied upon to be safe, are getting corrupted and set to empty values like undefined. This can cause other side effects and NPEs, potentially putting the UI in odd error states.

Currently, only able to reproduce in docker distributions. The root cause is related to the API calls not being set as rejected if they fail for whatever reason (e.g., searching for agents when the system index hasn't been initialized). In a local environment, this is caught, set as rejected, and the error is propagated. In a docker environment, it is being set as fulfilled state in redux, even if empty, leading to the corruption and downstream NPEs.

Further research is needed to identify the nuance.

[ohltyler]

Another instance where this causes odd behavior: on executing agentic search, if there is failures, the error message is returned plainly within the raw JSON response, instead of propagating as a rejected state, which would in turn set the redux error message, which would in turn properly render the search error in the EuiEmptyPrompt.