server: init functional tests (#5566)

* server: tests: init scenarios
 - health and slots endpoints
 - completion endpoint
 - OAI compatible chat completion requests w/ and without streaming
 - completion multi users scenario
 - multi users scenario on OAI compatible endpoint with streaming
 - multi users with total number of tokens to predict exceeds the KV Cache size
 - server wrong usage scenario, like in Infinite loop of "context shift" #3969
 - slots shifting
 - continuous batching
 - embeddings endpoint
 - multi users embedding endpoint: Segmentation fault #5655
 - OpenAI-compatible embeddings API
 - tokenize endpoint
 - CORS and api key scenario

* server: CI GitHub workflow


---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

examples/server/tests/features/environment.py

@@ -0,0 +1,67 @@
+import os
+import socket
+import subprocess
+import time
+from contextlib import closing
+from signal import SIGKILL
+
+
+def before_scenario(context, scenario):
+    print(f"\x1b[33;42mStarting new scenario: {scenario.name}!\x1b[0m")
+    port = 8080
+    if 'PORT' in os.environ:
+        port = int(os.environ['PORT'])
+    if is_server_listening("localhost", port):
+        assert False, "Server already started"
+
+
+def after_scenario(context, scenario):
+    if scenario.status == "failed":
+        if 'GITHUB_ACTIONS' in os.environ:
+            print(f"\x1b[33;101mSCENARIO FAILED: {scenario.name} server logs:\x1b[0m\n\n")
+            if os.path.isfile('llama.log'):
+                with closing(open('llama.log', 'r')) as f:
+                    for line in f:
+                        print(line)
+        if not is_server_listening(context.server_fqdn, context.server_port):
+            print("\x1b[33;101mERROR: Server stopped listening\x1b[0m")
+
+    if not pid_exists(context.server_process.pid):
+        assert False, f"Server not running pid={context.server_process.pid} ..."
+
+    print(f"stopping server pid={context.server_process.pid} ...")
+    context.server_process.kill()
+    # Wait few for socket to free up
+    time.sleep(0.05)
+
+    attempts = 0
+    while is_server_listening(context.server_fqdn, context.server_port):
+        print(f"stopping server pid={context.server_process.pid} ...")
+        os.kill(context.server_process.pid, SIGKILL)
+        time.sleep(0.1)
+        attempts += 1
+        if attempts > 5:
+            print(f"Server dangling exits, killing all {context.server_path} ...")
+            process = subprocess.run(['killall', '-9', context.server_path],
+                                     stderr=subprocess.PIPE,
+                                     universal_newlines=True)
+            print(process)
+
+
+def is_server_listening(server_fqdn, server_port):
+    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as sock:
+        result = sock.connect_ex((server_fqdn, server_port))
+        return result == 0
+
+
+def pid_exists(pid):
+    """Check whether pid exists in the current process table."""
+    import errno
+    if pid < 0:
+        return False
+    try:
+        os.kill(pid, 0)
+    except OSError as e:
+        return e.errno == errno.EPERM
+    else:
+        return True