[zlatanza] Spack exercise

[zezl7]

Description

This PR creates a base spack package for all releases of spack-exercise.

Changes

Mandatory

1. Created a Docker container based on the given image.
2. Created a base spack package using spack create.
3. Modified the package.py by removing all the FIX MEs and adding needed dependencies.

Optional

1. Added the main branch of spack-exercise as a version.
2. Added optional dependencies in both the CMakeLists.txt and package.py.

[IshaanDesai]

Good job, especially with the optional tasks 👏