Change text limit for duo workflow event message

What does this MR do and why?

• This field is used to store user input when Duo Workflow asks for follow-up information in the chat window.
• The previous limit was 255, which is much too constrained for user input.
• The new limit added here is 4096, which is somewhat arbitrary but we can always increase further later. Picked this to match the limit on the original workflow goal field.

References

• Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/523868
• Created with Duo Workflow, here was my input:

The duo_workflow_events database table has a messages column. The current text limit is 255 but should be increased to 4096. Increasing text limits on existing database columns can be safely achieved by first adding the new limit (with a different name), and then dropping the previous limit, example: class ChangeMaintainerNoteLimitInCiRunner < Gitlab::Database::Migration[2.1] disable_ddl_transaction! def up add_text_limit :ci_runners, :maintainer_note, 1024, constraint_name: check_constraint_name(:ci_runners, :maintainer_note, 'max_length_1K') remove_text_limit :ci_runners, :maintainer_note, constraint_name: check_constraint_name(:ci_runners, :maintainer_note, 'max_length') end def down # no-op: Danger of failing if there are records with length(maintainer_note) > 255 end end

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Screenshots or screen recordings

Not applicable, it's just a DB migration

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