feat(themes): add banner_message and banner_dismissible fields #38

Context

Add two fields to the theme level to support a dismissible banner displayed in Vido.

Changes

DB schema

• themes_translations.banner_message (text, nullable) — multilingual banner content (HTML)
• themes.banner_dismissible (boolean, default true) — whether the banner can be dismissed by the user

SQL

• themes_join view: aggregate banner_message from translations; select banner_dismissible from themes
• projects() function: expose both fields in the theme JSON output

Directus

• Field config for both fields in the admin UI

Swagger

• Add both fields to the theme schema in elasa-0.2.swagger.yaml