Compound web internationalisation

i18n has not been setup in @vector-im/compound-web As a result a few places have hardcoded strings.
We do not expect a large amounts of strings to exist in the project and as a result want to provide as lightweight of an i18n setup as possible.

**Suggestions:**

- Extract all hardcoded string into a JSON structure ressembling `en_EN.json` in the `matrix-react-sdk`
- Make the parent project override those string partially or comprehensively
- Always use english as a fallback language

Everything can be typed using the `matrix-web-i18n` package