gh-113471: Add custom default Content-Type to http.server (#113475)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: donBarbos <donbarbos@proton.me>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>