Add additional dirs to QA image Dockerignore

What does this MR do?

Adds the .git and node_modules directories to the QA image .dockerignore file.

While developing tests locally, my workflow using a built QA container for each test run was slowed down considerably after the QA image was changed to be built from the gitlab directory due to Docker collecting almost 1.5GB of build context before building the image. Some investigation found that the .git and node_modules directories were both over 500MB each and neither were included in the .dockerignore.

With this change, the build context is about 12MB instead.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team