ui: trim whitespaces when adding a subscription key

ui: trim whitespaces when adding a subscription key

users that add the correct subscription key just get unnecessarily
confused with a "value does not match the regex pattern" error if
they accidentally have a stray whitespace at the end or beginning
otherwise.

Switch to using our `proxmoxtextfield` component that provides a
`trimValue` config option since widget-toolkit commit 5d7d30d ("text
field: add trimValue config") that was made just for this case.

Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
 [ TL: reference widget toolkit commit ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>