[Filebeat] Cleanup channelContext and s3Context in s3 input

[kaiyan-sheng]

After common patterns are collected in github.com/elastic/go-concert, both channelContext and s3Context can be removed and replaced by the common pattern. This issue is to track the work mentioned in #12640 (comment) by @urso .

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[botelastic]

This issue doesn't have a Team:<team> label.

[urso]

In progress PR: #19756

[jsoriano]

I guess this was solved in #20005, so I am closing this. @kaiyan-sheng, please reopen if you think that this is still an issue.