Rename duplicate time field to be more descriptive and unique

[singholt]

Summary

This PR cherry-picks the commits from #4444 and runs go mod tidy && go mod vendor to resolve failing PR checks and merge the change before next ECS agent release.

---

Rename the log field used to show when an essential container was stopped, from time to ExecutionStoppedAt.
When logging that an essential container is stopped, we log the time that the container was stopped at. As all logs contain the fields level, time and msg, we end up with a duplicated time field, which some log processors are unable to handle - here is an example log:

{"level":"info","time":"2024-11-27T12:50:26Z","msg":"Essential container stopped; recording task stopped time","container":"ecs-appmesh-task-helper","task":"ad289555e6d74bf696db794907dcf1d4","time":"2024-11-27 12:50:26.023783669 +0000 UTC m=+89089.452265064"}

Implementation details

Renamed the extra logging field from time to ExecutionStoppedAt

Testing

Automated tests

New tests cover the changes: no

Description for the changelog

Enhancement: Renamed duplicated time field when logging container stopped events

Additional Information

Does this PR include breaking model changes? If so, Have you added transformation functions?
No

Does this PR include the addition of new environment variables in the README?
No

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.