Improve /about/executions endpoint

[MHHukiewitz]

The current implementation in lines 143-144 of #490:

return {
    "process": pid_info,
    **self.__dict__,
}

poses a risk of unintentionally overriding process data, as pointed out by @MHHukiewitz. This approach could lead to data loss or manipulation. @olethanh, while concerned about database compatibility, also notes irrelevant data appearing in the /about/executions endpoint. @hoh is open to improvements.

A revision is suggested to prevent potential data integrity issues and clean up the endpoint's output, possibly by introducing a separate field for self.__dict__. This aims to balance maintaining existing functionality with ensuring robust data handling.