Remove timestamp from slack chat replies

Proposal

When using a custom chatops reply with slash commands in the GitLab for Slack app, timestamps are included for each line that is returned.

For example, consider a job configured like so:

test:
  script:
    - |
      echo -e "section_start:$( date +%s ):chat_reply\r\033[0K\nTEST: PASS\nPASS: TEST\nYES: NO\nsection_end:$( date +%s ):chat_reply\r\033[0K"

When executed via /gitlab <project> run <job_name>, this results in the following output returned in Slack:

2026-01-27T20:14:50.403140Z 01O TEST: PASS
2026-01-27T20:14:50.403140Z 01O PASS: TEST
2026-01-27T20:14:50.403141Z 01O YES: NO
2026-01-27T20:14:50.403141Z 01O

We should either strip these timestamps by default for the sake of readability, or include an option that allows them to be toggled on/off.