Please add custom syntax names for debian/debputy.manifest

The debian/debputy.manifest file is a YAML based formats and it would be nice if vim would out of the box add syntax highlighting for it.

Most editors support YAML out of the box with a generic language server with schema-based logic. However, the debian/debputy.manifest has a lot of conditional logic that is not easily expressed by a schema. Therefore, it would be best if we got a custom syntax name for it, so debputy can be registered as language server for that format without affecting others.