switch from curl to ureq

switch from curl to ureq

Not only less code, we lose a whopping 29 libraries on linkage cruft:

> --- ldd.before  2022-01-26 19:03:25.759426164 +0100
> +++ ldd.after   2022-01-26 19:03:31.919529632 +0100
> @@ -5,36 +5,7 @@ librt.so.1
>  libzstd.so.1
>  libc.so.6
>  /lib64/ld-linux-x86-64.so.2
> -libcurl-gnutls.so.4
>  libgcc_s.so.1
>  libpthread.so.0
>  libm.so.6
>  libdl.so.2
> -libnghttp2.so.14
> -libidn2.so.0
> -librtmp.so.1
> -libssh2.so.1
> -libpsl.so.5
> -libnettle.so.8
> -libgnutls.so.30
> -libgssapi_krb5.so.2
> -libldap_r-2.4.so.2
> -liblber-2.4.so.2
> -libbrotlidec.so.1
> -libz.so.1
> -libunistring.so.2
> -libhogweed.so.6
> -libgmp.so.10
> -libgcrypt.so.20
> -libp11-kit.so.0
> -libtasn1.so.6
> -libkrb5.so.3
> -libk5crypto.so.3
> -libcom_err.so.2
> -libkrb5support.so.0
> -libresolv.so.2
> -libsasl2.so.2
> -libbrotlicommon.so.1
> -libgpg-error.so.0
> -libffi.so.7
> -libkeyutils.so.1

IOW.: curl is really nice for a CLI tool and super powerful library,
but way to much overkill for simple HTTP requests (not even TLS) we
need here.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>