Function create_or_lookup_mailinglist

async fn create_or_lookup_mailinglist(
    context: &Context,
    allow_creation: bool,
    list_id_header: &str,
    mime_parser: &MimeMessage,
) -> Result<Option<(ChatId, Blocked)>>

Create or lookup a mailing list chat.

list_id_header contains the Id that must be used for the mailing list and has the form Name <Id>, <Id> or just Id. Depending on the mailing list type, list_id_header was picked from ListId:-header or the Sender:-header.

mime_parser is the corresponding message and is used to figure out the mailing list name from different header fields.