feat(labels):Add common testcontainers labels (#519)

- Closes:
#510

Aligns with other test container projects

Example: I also contribute to go project, those labels look like

```
  "maintainer": "docker@couchbase.com",
  "org.opencontainers.image.ref.name": "ubuntu",
  "org.opencontainers.image.version": "20.04",
  "org.testcontainers": "true",
  "org.testcontainers.lang": "go",
  "org.testcontainers.sessionId": "e01aa90cfb75a53fbd53776b8c2eb84a99e3f1c8a7103512468cf75735421176",
  "org.testcontainers.version": "0.30.0"
```

Java appears to do similar -
https://github.com/testcontainers/testcontainers-java/blob/main/core/src/main/java/org/testcontainers/DockerClientFactory.java#L51

I didn't add in the image info as there wasn't an obvious way to get a
handle on that nor obvious value.
Another thing is that the python prefers `session-id` to `sessionId`.
I'm not sure if there are any cross-language reasons to have those be
identical, I left it alone.

Also this adds in tests for the label code.

---------

Co-authored-by: bstrausser <bstrausser@locusrobotics.com>
Co-authored-by: David Ankin <daveankin@gmail.com>

Author: 3 people

core/testcontainers/core/labels.py

@@ -1,17 +1,29 @@
+import importlib
 from typing import Optional
 from uuid import uuid4
 
 from testcontainers.core.config import testcontainers_config as c
 
 SESSION_ID: str = str(uuid4())
+TESTCONTAINERS_NAMESPACE = "org.testcontainers"
+
+LABEL_TESTCONTAINERS = TESTCONTAINERS_NAMESPACE
 LABEL_SESSION_ID = "org.testcontainers.session-id"
+LABEL_VERSION = "org.testcontainers.version"
 LABEL_LANG = "org.testcontainers.lang"
 
 
 def create_labels(image: str, labels: Optional[dict[str, str]]) -> dict[str, str]:
     if labels is None:
         labels = {}
+    else:
+        for k in labels:
+            if k.startswith(TESTCONTAINERS_NAMESPACE):
+                raise ValueError("The org.testcontainers namespace is reserved for interal use")
+
     labels[LABEL_LANG] = "python"
+    labels[LABEL_TESTCONTAINERS] = "true"
+    labels[LABEL_VERSION] = importlib.metadata.version("testcontainers")
 
     if image == c.ryuk_image:
         return labels

core/tests/test_labels.py

@@ -0,0 +1,58 @@
+from testcontainers.core.labels import (
+    LABEL_LANG,
+    LABEL_SESSION_ID,
+    LABEL_TESTCONTAINERS,
+    LABEL_VERSION,
+    create_labels,
+    TESTCONTAINERS_NAMESPACE,
+)
+import pytest
+from testcontainers.core.config import RYUK_IMAGE
+
+
+def assert_in_with_value(labels: dict, label: str, value: str, known_before_test_time: bool) -> None:
+    assert label in labels
+    if known_before_test_time:
+        assert labels[label] == value
+
+
+testdata = [
+    (LABEL_LANG, "python", True),
+    (LABEL_TESTCONTAINERS, "true", True),
+    (LABEL_SESSION_ID, "some", False),
+    (LABEL_VERSION, "some", False),
+]
+
+
+@pytest.mark.parametrize("label,value,known_before_test_time", testdata)
+def test_containers_creates_expected_labels(label, value, known_before_test_time):
+    actual_labels = create_labels("not-ryuk", None)
+    assert_in_with_value(actual_labels, label, value, known_before_test_time)
+
+
+def test_containers_throws_on_namespace_collision():
+    with pytest.raises(ValueError):
+        create_labels("not-ryuk", {TESTCONTAINERS_NAMESPACE: "fake"})
+
+
+def test_containers_respect_custom_labels_if_no_collision():
+    custom_namespace = "org.foo.bar"
+    value = "fake"
+    actual_labels = create_labels("not-ryuk", {custom_namespace: value})
+    assert_in_with_value(actual_labels, custom_namespace, value, True)
+
+
+def test_if_ryuk_no_session():
+    actual_labels = create_labels(RYUK_IMAGE, None)
+    assert LABEL_SESSION_ID not in actual_labels
+
+
+def test_session_are_module_import_scoped():
+    """
+    Asserts that sessions are a module-level variable and don't differ between invocation
+    """
+    first_labels = create_labels("not-ryuk", None)
+    second_labels = create_labels("not-ryuk", None)
+    assert LABEL_SESSION_ID in first_labels
+    assert LABEL_SESSION_ID in second_labels
+    assert first_labels[LABEL_SESSION_ID] == second_labels[LABEL_SESSION_ID]