Add possibility to translate the channel namespace

Problem/Motivation

Currently it does not seem to be possible to for example to translate the channel description.

<channel>
    <title>Feed title</title>
    <link>https://domain.com/rss</link>
    <description><![CDATA[Test description]]></description>

There is the possibility to translate the feed title from the display options but I cannot seem to find anyway to translate the channel description.

Proposed resolution

We should make the channel fields also translatable.

Remaining tasks

1. Add translate possibility.
2. Add tests.

User interface changes

Add an UI where you can translate the channel settings like description.

API changes

TBD.

Data model changes

TBD.