feat(dev): add gdb

Required for local or remote debugging.

Closes: zmkfirmware/zmk-docker#7
PR: zmkfirmware/zmk-docker#54

.github/workflows/containers.yml

@@ -402,6 +402,8 @@ jobs:
         run: pager --version && [[ $PAGER = "less" ]] && true || false
       - name: Test ssh
         run: ssh -V
+      - name: Test gdb
+        run: gdb --version
       - name: Stop container
         shell: bash
         run: docker stop candidate

Dockerfile

@@ -50,6 +50,7 @@ RUN \
   && apt-get -y install --no-install-recommends \
   clang-format \
   g++-multilib \
+  gdb \
   gpg \
   gpg-agent \
   less \