Pass an explicit context path to docker build in `build_ci_image`

What does this MR do?

It ensures that the context path passed to docker build is explicit and doesn't rely on relative paths.

Why was this MR needed?

To make the context passed to docker build easier to understand.

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

Closes #25873 (closed)