disable autocomplete for Token field on chat slash command config page

Open Simon Knox requested to merge 27814-token-autocomplete-off into master

What does this MR do?

Stop browser prompting to prefill the Token field on Slack/Mattermost command config page

Are there points in the code the reviewer needs to double check?

Screenshots (if relevant)


Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #27814 (moved)

Edited by Simon Knox