chore: move apt packages from main Dockerfile into base image layer (#41630)

## Summary
- Moves `software-properties-common`, `tar`, `zstd`, `openssh-client`,
and the `git-core` PPA upgrade from the main `Dockerfile` into
`deploy/docker/base.Dockerfile`
- Consolidated into the existing single apt `RUN` block (alongside
MongoDB/PostgreSQL installs) to keep everything in one layer rather than
adding a new layer

## Test plan
- [ ] Trigger a base image build and verify the packages are present in
the resulting image
- [ ] Verify the main image build succeeds with the apt block removed

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Reorganized Docker build setup and consolidated system dependency
installation (including version control, archive, compression, and SSH
tools) into the container build process.
  * Added an extra software repository used during builds.
* CI build triggers expanded to run when container configuration
changes.
  * No user-facing feature or behavior changes.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

<!-- This is an auto-generated comment: Cypress test results  -->
> [!WARNING]
> Tests have not run on the HEAD
02c54bd639e4ddedfe2bdcd4caec7c7414c85b98 yet
> <hr>Tue, 17 Mar 2026 21:04:55 UTC
<!-- end of auto-generated comment: Cypress test results  -->

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>