Dev Docker: add php extensions needed for unit testing and code coverage

[kraftbj]

The new Dev Docker container need additional php extensions for WordPress (for unit testing/WorDBless) and code coverage.

Proposed changes:

• Add various PHP extensions.
• Adds a npm_config_update_notifier env var to prevent PNPM from alerting to update the in-docker pnpm version.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

#41057 (comment)

Does this pull request change what data or activity we track or use?

No.

Testing instructions:

• BUILD_LOCAL=1 jp test php packages/image-cdn -v
• BUILD_LOCAL=1 jp test coverage packages/image-cdn (or any other package with PHP code coverage.
• Note: may need to delete local copies of the image within Docker to force the new build.

[github-actions]

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[kraftbj]

I'll update the PR description. This snuck in. It's to disable the prompt to update pnpm when running jp commands. Since each container is destroyed after use, even if someone updated pnpm within the docker container, the image would still have 9.15.0.

I struggled to find documentation of this related to pnpm, but npm added it via npm/cli#1632 and pnpm claims to follow npm's update notification framework. In testing, it seemed to work. At worst, it does nothing.

[anomiex]

Do we want DEBIAN_FRONTEND set inside the image itself? From https://docs.docker.com/reference/dockerfile/#env

Environment variable persistence can cause unexpected side effects. For example, setting ENV DEBIAN_FRONTEND=noninteractive changes the behavior of apt-get, and may confuse users of your image.

If an environment variable is only needed during build, and not in the final image, consider setting a value for a single command instead:

RUN DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install -y ...

Or using ARG, which is not persisted in the final image:

ARG DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install -y ...

[anomiex]

Let's do it!