Add bash completion for snap (#2058)

snapcraft.yaml

@@ -1,4 +1,4 @@
-base: core20
+base: core22
 confinement: classic
 contact: casey@rodarmor.com
 description: Just is a handy way to save and run project-specific commands.
@@ -15,6 +15,7 @@ website: https://just.systems
 apps:
   just:
     command: bin/just
+    completer: just.bash
 
 parts:
   just:
@@ -23,3 +24,9 @@ parts:
     source-tag: '1.2.0'
     source-type: git
     source: https://github.com/casey/just
+
+  completions:
+    plugin: dump
+    source: completions
+    stage:
+      - just.bash