feat: Allow skipping setup (#414)

If a user is invoking the action multiple times then the trivy binary
gets installed multiple times.  Users can avoid this by managing the
installation themselves and setting the skip-setup input to true, or by
letting the action install in on their first invocation and then setting
skip-setup to true on subsequent invocations

Co-authored-by: simar7 <1254783+simar7@users.noreply.github.com>

action.yaml

@@ -103,11 +103,16 @@ inputs:
     description: 'Used to specify whether caching is needed. Set to false, if you would like to disable caching.'
     required: false
     default: 'true'
+  skip-setup-trivy:
+    description: 'skip calling the setup-trivy action to install trivy'
+    required: false
+    default: 'false'
 
 runs:
   using: 'composite'
   steps:
     - name: Install Trivy
+      if: ${{ inputs.skip-setup-trivy == 'false' }}
       uses: aquasecurity/setup-trivy@v0.2.1
       with:
         version: ${{ inputs.version }}