Documentation for slot params shows bad example about owl

[sdegueldre]

This is kind of a general problem with string literals in Owl templates. While I'm not opposed to reworking some sections of the Owl docs to avoid actively promoting this pattern, sometimes it just makes the point we're trying to make more clearly as it cuts down on the cruft. We can probably get around this issue in most places by passing technical strings instead though.

I think it would be helpful to have a big fat warning in the Odoo docs about Owl components: "String literals in template cannot be translated. You should never put any user-facing string within quotes in a template anywhere".

There is also a page dedicated to translations in the Owl docs, which could use some improvement to clarify what things won't be translated: https://github.com/odoo/owl/blob/master/doc/reference/translations.md