add internal remote config patch tool

[LukasPaczos]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1208671518894266/task/1210708742763735

Description

Adds tooling to locally patch remote config. Read the details in the new README file in the diff.

Steps to test this PR

1. Create a privacy-config/privacy-config-internal/local-patch-file/test_patch.json file with this content:

[
  {
    "op": "replace",
    "path": "/features/aiChat/state",
    "value": "disabled"
  }
]

2. Create a privacy-config/privacy-config-internal/local.properties file with this content:

config_patches=privacy-config/privacy-config-internal/local-config-patches/test_patch.json

3. Clean install the app.
4. Verify Duck.ai is disabled and that Settings -> Duck.ai is gone.
5. Update the patch file to:

[
  {
    "op": "replace",
    "path": "/version",
    "value": "2752244802866"
  },
  {
    "op": "remove",
    "path": "/features/aiChat/hash"
  }
]

6. Relaunch the app (without clean installing it). This will download the production config and force update the feature because of the bumped version number and mismatching hash.
7. Verify Duck.ai is enabled and that Settings -> Duck.ai is available.
8. Update the test_patch.json to disable Duck.ai again and bump version:

[
  {
    "op": "replace",
    "path": "/features/aiChat/state",
    "value": "disabled"
  },
  {
    "op": "remove",
    "path": "/features/aiChat/hash"
  },
  {
    "op": "replace",
    "path": "/version",
    "value": "3752244802866"
  }
]

9. Relaunch the app (without clean installing it).
10. Verify Duck.ai is disabled and that Settings -> Duck.ai is gone.

[LukasPaczos]

All interceptors are currently added in default order, sorted by class name. If I assign a low priority to this interceptor without changing the others, it would run first, since it would be the only one with a defined priority. I tried giving all plugins the same priority (to preserve class name sorting as PriorityKey docs suggest) and setting this interceptor last, but the build fails due to duplicate priority keys, despite what the docs say.

I don’t want to risk changing any production behavior, so it’s fine if this interceptor doesn’t run last for now. If it ever becomes a problem, we can revisit.