Function get_file_base64s

pub async fn get_file_base64s(
    markdown: &str,
    regex: Regex,
    guess_mime_type: fn(url: &str) -> String,
) -> Vec<Option<MatchedFiles>>

regex must have a Regex with atleast 1 capture group with file URL as first capture group
Else it PANICS mime_type_guess is used to detect mimi_type of URL pointing to file system or web resource with no “Content-Type” header.