Add TLS 1.3 early data examples

[julek-wolfssl]

Introduces client and server examples that demonstrate the use of
TLS 1.3 early data (0-RTT) with session resumption.

The client example performs an initial handshake to obtain a session
ticket, then reconnects and sends early data. The server example
receives early data and sends back a reply.

DTLS 1.3 examples depend on wolfSSL/wolfssl#9367

[dgarske]

Please add these to the tls/README.md and dtls/README.md

Also if wolfSSL isn't built with --enable-earlydata then you get:

gcc -o client-tls13-earlydata  client-tls13-earlydata.c -Wall -I/usr/local/include -Os -L/usr/local/lib -lm -lwolfssl
client-tls13-earlydata.c: In function ‘main’:
client-tls13-earlydata.c:131:33: warning: implicit declaration of function ‘wolfSSL_SSL_get0_session’; did you mean ‘wolfSSL_get1_session’? [-Wimplicit-function-declaration]
  131 |     if (!wolfSSL_SessionIsSetup(wolfSSL_SSL_get0_session(ssl))) {
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~
      |                                 wolfSSL_get1_session
client-tls13-earlydata.c:131:33: warning: passing argument 1 of ‘wolfSSL_SessionIsSetup’ makes pointer from integer without a cast [-Wint-conversion]
  131 |     if (!wolfSSL_SessionIsSetup(wolfSSL_SSL_get0_session(ssl))) {
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                                 |
      |                                 int
In file included from client-tls13-earlydata.c:35:
/usr/local/include/wolfssl/ssl.h:2903:57: note: expected ‘WOLFSSL_SESSION *’ but argument is of type ‘int’
 2903 | WOLFSSL_API int wolfSSL_SessionIsSetup(WOLFSSL_SESSION* session);
      |                                        ~~~~~~~~~~~~~~~~~^~~~~~~
client-tls13-earlydata.c:134:37: warning: passing argument 1 of ‘wolfSSL_SessionIsSetup’ makes pointer from integer without a cast [-Wint-conversion]
  134 |         if (!wolfSSL_SessionIsSetup(wolfSSL_SSL_get0_session(ssl))) {
      |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                                     |
      |                                     int
/usr/local/include/wolfssl/ssl.h:2903:57: note: expected ‘WOLFSSL_SESSION *’ but argument is of type ‘int’
 2903 | WOLFSSL_API int wolfSSL_SessionIsSetup(WOLFSSL_SESSION* session);
      |                                        ~~~~~~~~~~~~~~~~~^~~~~~~
client-tls13-earlydata.c:181:11: warning: implicit declaration of function ‘wolfSSL_write_early_data’; did you mean ‘wolfSSL_set_ex_data’? [-Wimplicit-function-declaration]
  181 |     ret = wolfSSL_write_early_data(ssl, EARLY_DATA_MSG, EARLY_DATA_MSG_LEN, &earlyDataSent);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~
      |           wolfSSL_set_ex_data
/usr/bin/ld: /tmp/cclNqs3t.o: in function `main':
client-tls13-earlydata.c:(.text.startup+0x183): undefined reference to `wolfSSL_SSL_get0_session'
/usr/bin/ld: client-tls13-earlydata.c:(.text.startup+0x1a8): undefined reference to `wolfSSL_SSL_get0_session'
/usr/bin/ld: client-tls13-earlydata.c:(.text.startup+0x2eb): undefined reference to `wolfSSL_write_early_data'
collect2: error: ld returned 1 exit status
make: *** [Makefile:110: client-tls13-earlydata] Error 1