Tweak in_app rules for events from Python SDK

[sentrivana]

When viewing a stacktrace in Sentry, frames are marked as either in_app or not in_app. Non-in-app frames are collapsed by default. The original in_app decision comes from the SDK; however, at the moment Sentry can't rely on the in_app decision from the SDK and has rules for overriding it.

Two things we can do about this:

1. On the Sentry side, remove the redundant checks that set a frame as not in-app if the package is coming from site-packages or dist-packages. We already check this on the SDK side. Having this rule on the server side means that it sometimes overrides a higher prio decision (e.g., the user explicitly set their in_app_include to include the module).
2. On the SDK side, look into frames with unexpected in_app values and fix the underlying issues. Tracked here: Improve in_app detection sentry-python#3682

[armenzg]

Given the current event [1] we want to end up with this:

               "abs_path": "/app/python/site-packages/foo/bar.py",
-              "in_app": false,
-              "data": {
-                "orig_in_app": 1
+              "in_app": true
              }

[1]

{
  "exception": {
    "values": [
      {
        "stacktrace": {
          "frames": [
            {
              "abs_path": "/app/python/site-packages/foo/__main__.py",
              "in_app": false
            },
            {
              "abs_path": "/app/python/site-packages/click/core.py",
              "in_app": false
            },
            {
              "abs_path": "/app/python/site-packages/foo/bar.py",
              "in_app": false,
              "data": {
                "orig_in_app": 1
              }
            }
          ]
        }
      }
    ]
  }
}

[armenzg]

We need to skip applying the rule if in_app is already set to True since the rules were only added a year ago (PR).