View attachments

Current situation

A workflow can produce attachments, but those are not easily accessible from opentf-ctl: they are visible in the events, but that is all.

Desired outcome

A way to easily list attachments produced by a workflow. Something like opentf-ctl get workflow xxx --show attachments (any other name for the command-line option is fine, this is just an example) that gives:

...
[2021-10-13T17:18:33] [job 9ea3be45-ee90-4135-b47f-e66e4f793383] Requesting execution environment providing ['windows', 'robotframework'] for job keyword-driven
[2021-10-13T17:18:33] [job 9ea3be45-ee90-4135-b47f-e66e4f793383] Running actionscheckoutv2
[2021-10-13T17:18:33] [job 9ea3be45-ee90-4135-b47f-e66e4f793383]  Running command: git clone https...
[2021-10-13T17:18:33] [job 9ea3be45-ee90-4135-b47f-e66e4f793383]    Produced attachment 123ae-... (output.xml)
[2021-10-13T17:18:33] [job 9ea3be45-ee90-4135-b47f-e66e4f793383]    Produced attachment 56ji3-... (result.html)
[2021-10-13T17:18:37] [job 9ea3be45-ee90-4135-b47f-e66e4f793383] Running command: dir
...

Attachments info is interspersed with commands, so that their origin is clear.

It includes attachments resulting from ExecutionResult and WorkflowResult events.