Add Snowplow event tracker and client wrapper

What does this MR do and why?

This adds the ability to track code suggestions events using Python Snowplow tracker.

• Introduce Snowplow standard synchronous tracker and emitter
• Introduce some environment variables to configure Snowplow tracking
  • SNOWPLOW_ENABLED - default to false, only enable in prod
  • SNOWPLOW_ENDPOINT - default to none, only set in prod
• Add specs and ensure the dependency is stubbed
• Use AsyncEmitter instead of synchronous emitter

Related to #192 (closed)

How to validate and test locally

We need to setup Snowplow Micro locally to instropect the event emitted from Model Gateway.

1. Clone Snowplow Micro repo
2. Run bash ./snowplow-micro.sh
3. In another terminal session, build and run a Model Gateway container

   $ docker buildx build --platform linux/amd64 -t code-suggestions-api:dev .
   $ docker run -it --platform linux/amd64 --rm -v $PWD:/app -it code-suggestions-api:dev bash
   $ poetry run python

4. Run the follow script in the Poetry shell session

   >>> from codesuggestions.tracking import *
   None of PyTorch, TensorFlow >= 2.0, or Flax have been found. Models won't be available and only tokenizers, configuration and file/data utilities can be used.
   >>> client = SnowplowClient(configuration=SnowplowClientConfiguration(endpoint="http://host.docker.internal:9090"))
   INFO:snowplow_tracker.emitters:Emitter initialized with endpoint http://host.docker.internal:9090/com.snowplowanalytics.snowplow/tp2
   >>> client.track(SnowplowEvent(context=SnowplowEventContext(request_counts=[RequestCount(requests=1, errors=0, accepts=1, lang="python", model_engine="vertex-ai", model_name="code-gecko")],prefix_length=2048, suffix_length=1024, language="python", user_agent="vs-code-gitlab-workflow", gitlab_realm="saas")))
   INFO:snowplow_tracker.emitters:Attempting to send 1 events
   INFO:snowplow_tracker.emitters:Sending POST request to http://host.docker.internal:9090/com.snowplowanalytics.snowplow/tp2...

5. Verify the events from Snowplow micro via http://localhost:9090/micro/good

   $ curl -s http://localhost:9090/micro/good | jq .[0].rawEvent
   {
     "api": {
       "vendor": "com.snowplowanalytics.snowplow",
       "version": "tp2"
     },
     "parameters": {
       "e": "se",
       "eid": "e86c72b2-8272-476c-98b2-0a9a4b575e07",
       "aid": "gitlab_ai_gateway",
       "cx": "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",
       "tna": "gl",
       "stm": "1691159810000",
       "tv": "py-1.0.1",
       "se_ac": "suggestions_requested",
       "se_ca": "code_suggestions",
       "p": "pc",
       "dtm": "1691159810428"
     },
     "contentType": "application/json",
     "source": {
       "name": "snowplow-micro-1.7.2-stdout$",
       "encoding": "UTF-8",
       "hostname": "host.docker.internal"
     },
     "context": {
       "timestamp": "2023-08-04T14:36:50.597Z",
       "ipAddress": "172.17.0.1",
       "useragent": "python-requests/2.31.0",
       "refererUri": null,
       "headers": [
         "Timeout-Access: <function1>",
         "Host: host.docker.internal:9090",
         "User-Agent: python-requests/2.31.0",
         "Accept-Encoding: gzip, deflate",
         "Accept: */*",
         "Connection: keep-alive",
         "application/json"
       ],
       "userId": "e4d1fce8-2737-4e5d-af85-878fda9a3267"
     }
   }

6. The context payload cx can be Base64-decoded

   ❯ echo -n "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" | base64 --decode
   {"schema": "iglu:com.snowplowanalytics.snowplow/contexts/jsonschema/1-0-1", "data": [{"schema": "iglu:com.gitlab/code_suggestions_context/jsonschema/1-0-0", "data": {"request_counts": [{"requests": 1, "errors": 0, "accepts": 1, "lang": "python", "model_engine": "vertex-ai", "model_name": "code-gecko"}], "prefix_length": 2048, "suffix_length": 1024, "language": "python", "user_agent": "vs-code-gitlab-workflow", "gitlab_realm": "saas"}}]}