Feature request: set custom form fields on incidents create/update

[minkimipt]

Use case

Creating an incident or maintenance from a script with the workspace's custom form fields filled in, the same as the UI dialog.

What's missing

incidents create / incidents update have flags for built-in attributes (--services, --types, --environments, --teams, …) but no way to set custom form fields. There is no --field style flag, and custom field values aren't read back by incidents get either.

Why it matters

Workspaces use required custom fields to drive status-page templates and workflows — in ours, a planned maintenance needs a software version and a rollout date, and the status-page announcement template interpolates them (the version builds a changelog link). A CLI-created incident without them either fails the workspace's requirements or publishes a broken announcement, so the create step still has to go through the UI.

Proposed

rootly incidents create --title="..." --field sw_version=2.30.2 --field rollout_date=2026-10-05
rootly incidents update <id> --field rollout_date=2026-10-06
rootly incidents get <id> --format=json   # includes custom field values

Keyed by the form field slug, repeatable. Discovery could follow the existing pattern (rootly form-fields list), like services list / teams list.