QUIC Support

[davidBar-On]

• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies:
  master 3.20+

• Issues fixed (if any): Should we provide QUIC support when it is done? #1017

• Brief description of code changes (suitable for use as a commit message):

Adding QUIC support to iperf3, using ngtcp2 library (documentation), with openssl support. QUIC tests are run by setting either -q or --quic option.

Code development was done using ngtcp2 tag 1.20 and openssl 3.6 versions. Hopefully later versions of these libraries will be backward compatible.

Note that ./bootstrap.sh; ./configure should run before the first make (to include the ngtcp2 library and new source files).

Briefly, on Ubuntu Linux I built ngtcpt2 library with openssl support by (see also the ngtcp2 documentation, but it does not include instructions for using openssl):

1. Download ngtcp2 repository (using git clone).
2. Run: ./configure --with-openssl; make -j$(nproc) check; sudo make install
3. Copy "ssl" and "crypto" libs from /usr/lib/lib64 to /usr/lib/x86_64-linux-gnu (at least I had to that in my computer)

Note that the openssl key and certificate are per-defined statically in the code and there is no need to create them.