Change external projects download method to https
Change external projects download method to https

Since CMake FetchContent with git would clone the whole repository,
using http to download only specific version would save a lot of
time and space.

Signed-off-by: Yibai Zhang <5b43591ea83735bdc4b2cc883401252dffce7c91@gmail.com>

whoshuu/cpr,whoshuu/cpr,whoshuu/cpr