add test FEATURE test_hello for capability advertisement

[vjardin]

Verify that YANG 1.0 modules appear in the server hello capabilities and that YANG 1.1 modules do not, per RFC 7950 section 1.1:

o  A server advertises support for YANG 1.1 modules by using
      ietf-yang-library [[RFC7895](https://datatracker.ietf.org/doc/html/rfc7895)] instead of listing them as
      capabilities in the <hello> message.

YANG 1.1 modules are discoverable via ietf-yang-library, whose operational data is auto-generated by sysrepo.

[vjardin]

see CESNET/libnetconf2#587

[vjardin]

record the test:

LD_LIBRARY_PATH=/home/vjardin/dev/cesnet_test/lib ctest -R test_hello --output-on-failure
Test project /home/vjardin/dev/netopeer2/build
    Start 18: test_hello
1/3 Test #18: test_hello .......................   Passed    3.24 sec
    Start  2: tests_kill_server
2/3 Test  #2: tests_kill_server ................   Passed    0.01 sec
    Start  3: tests_clear_state
3/3 Test  #3: tests_clear_state ................   Passed    0.00 sec

[michalvasko]

Honestly, I do not see much added value in this test.