Update electron statuses for `AWSBracketExecutor`

[kessler-frost]

Once separation of workflow and electron statuses is done, the electron level statuses need to be updated to accommodate executor dependent statuses. In this case the following status definitions will be updated:

• REGISTERING - Uploading task and creating Bracket job definition

• PENDING_BACKEND - Corresponds to Bracket job state Created

• RUNNING - Corresponds to Bracket job state Running

• COMPLETING - Bracket job is in the Stopped state, results files being retrieved, temporary files are being deleted

For the end state, there is a separate class called EndState and contains all possible end state statuses like COMPLETED, FAILED, etc. and thus does not need to be added to the executor dependent status.

Acceptance Criteria:

• Above mentioned statuses need to be updated inside the local executor
• Tests need to be added to verify if those definitions are as expected