Add Headful browsing to Inspect's Web Tooling

[cmathw]

This PR contains:

• New features
• Changes to dev-tools e.g. CI config / github tooling
• Docs
• Bug fixes
• Code refactor

What is the current behavior? (You can also link to an open issue here)

The web_browser tooling only makes use of headless browser, it is not possible to view this browser graphically in real-time.

What is the new behavior?

This PR implements headful browsing, allowing users to view an agent's interactions with the browser in real time via a VNC viewer.

Tests have been added for this new behaviour in test_playwright_crawler. These are essentially just parameterising playwright's headless flag to test both True and False, instead of just True originally.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

This PR should be accompanied by an update to the image (aisiuk/inspect-web-browser-tool) hosted at Dockerhub for web_browser tooling. This PR's implementation defaults to headless mode. For users making use of web_browser tooling who are not aware of this PR, there should be no downstream impacts.

Other information:

This PR's implementation makes use of a layered Dockerfile approach, the user selects a build target in their task's docker-compose file. For example, in the examples/browser/compose.yaml file, the user can choose headful browsing with:

services:
  default:
    build:
      context: ../../src/inspect_ai/tool/_tools/_web_browser/_resources
      dockerfile: Dockerfile
      target: headful
    ports:
      - "127.0.0.1:5900:5900"

If a target is not specified, or it is specified as headless the Dockerfile will build the headless image. In this instance, it is not necessary to specify the 127.0.0.1:5900:5900 port mapping either (this is only needed for VNC viewing).

This PR achieves this broadly by:

• Replacing the playwright headless flag with an environment variable instead of hardcoding to True (i.e. the "HEADLESS" environment variable).
• Each Docker build set this "HEADLESS" environment variable depending on the target chosen by the user. The Dockerfile uses a layered approach such that only the layer's necessary for each respective build are included in the image.
• The same entrypoint.sh file is copied across into the web_browser container irrespective of target, it uses the "HEADLESS" environment variable to dictate the actions taken at container start.

Note: When running tests, a chromium browser will open/close for the headful tests, if necessary I'm open to adding decorators to these tests so they are only run when specified.

[cmathw]

Closing this PR as it's being moved to the upstream repository here.