fix #4271: api-viewer: display nested formats instead of [object Object]

fix #4271: api-viewer: display nested formats instead of [object Object]

I tried to keep the format as close to the HTML docs as possible, but
there are a few discrepancies between HTML docs and how this patch
displays parameters, instead of:
- <enum>,the enum variants are displayed. [1]
- <0|1>, <boolean> is displayed.

[1] The HTML docs explain parameters after the initial format string,
which the GUI doesn't (and there's no space for that). Showing the
variants inline is the easiest way to not loose information here.

Signed-off-by: Matthias Heiserer <m.heiserer@proxmox.com>