Upgrade component

Upgrades one component (plugin, theme or WordPress core) to its newest version on the selection: one `manager.upgrade`/`manager.safe_upgrade` Site Action per accepted site.\n\nBody parameters:\n- `sites` (integer array, required): exact ids, 1 to 200.\n- `action` (string, default `safe_upgrade`): `safe_upgrade` (backup, upgrade, visual check, automatic rollback) or `upgrade` (direct, no rollback).\n- `is_manual` (boolean `1`/`0`, default `0`): `action: safe_upgrade` only; `1` stops each site at `REQUIRES_ACTION` for a human verdict instead of auto-validating.\n- `clean_cache` (boolean `1`/`0`, default: the account's updates setting): clear each site's cache after upgrading.\n- `scheduled_at` (string, ISO 8601 datetime): must be in the future (`after:now`); omit to run now.\n\n202 with the created `site-actions` documents and `meta.skipped`.\n\n- **422**: `sites` missing/empty/over 200/unknown id; `scheduled_at` not in the future.\n- **404**: `{component}` does not exist or is not reachable from the token's organization.\n- **403**: a read-only token.