ext,github,tests: Update DRAMSys tests to v5.0 and handle new dependencies (#577)

#525 Updated DRAMSys to v5.0. This PR further improves v5.0
inforporation into gem5 by better managing its new dependencies and
updating the DRAMSys tests to use v5.0.

This PR:

1. Adds a check which throws warning if DRAMSys cannot be build due to a
missing `cmake` instead of failing with a build error. `cmake` is not a
hard gem5 requirement. It is only required to build DRAMSys in the cases
it is required. It is therefore prudent to not fail a build in cases
`cmake` is not present on the host system.
2. Updates the "all-dependency" Docker images to include the optional
dependencies `git-lfs` (needed to clone the DRAMSys repo when running
the command outlined in ext/dramsys/README -- introduced in #525) and
`cmake` (needed to build DRAMSys).
3. Updates the Weekly workflow's `dramsys-tests`' `Checkout DRAMSys` job
to clone DRAMSys in the same manner as outlined in ext/dramsys/README.
This ensures the `dram-systests` test the instructions we give users.
4. `.gitignore` is added to ext/dramsys to ignore the
ext/dramsys/DRAMSys directory when cloned for building and integration
into gem5.

(2.) Should fix our failing weekly tests:
https://github.com/gem5/gem5/actions/runs/6912511984/job/18808339821 and
(3.) will ensure the changes introduced in #525 are tested.

.github/workflows/weekly-tests.yaml

@@ -89,11 +89,7 @@ jobs:
 
             - name: Checkout DRAMSys
               working-directory: ${{ github.workspace }}/ext/dramsys
-              run: |
-                  git clone https://github.com/tukl-msd/DRAMSys DRAMSys
-                  cd DRAMSys
-                  git checkout -b gem5 09f6dcbb91351e6ee7cadfc7bc8b29d97625db8f
-                  git submodule update --init --recursive
+              run: git clone https://github.com/tukl-msd/DRAMSys --branch v5.0 --depth 1 DRAMSys
 
       # gem5 is built separately because it depends on the DRAMSys library
             - name: Build gem5