[FIX] website: exclude non installable theme on configurator

Exclude non installable theme from the configurator suggested themes.
Also, exclude themes which are found in the database (sql) but not in
the manifest (files/sources). This was reported after migration where
`theme_beauty_sale` was still in the database but did not exists
anymore.

Note that in prior versions, this was causing a `KeyError`.

closes odoo/odoo#92167

X-original-commit: 6e4faeb136e123e09d74cde06c47f7c822b1fd19
Signed-off-by: Romain Derie (rde) <rde@odoo.com>