Updated the Cluster Agent Token table heading

What does this MR do and why?

In this MR we change the Agent Token table column heading from 'Last used' to 'Last contact' so that it is more consistent with the Cluster Agent table.

Screenshots or screen recordings

Before	After

How to set up and validate locally

To validate the change locally:

1. Add the cluster agent following the instruction
2. You can also follow this instructions
3. Go to Infrastructure -> Kubernetes clusters view and select GitLab Agent managed clusters tab.
4. Click on the Agent name to get to the Agent Token page.
5. Verify table columns names.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

ee/app/assets/javascripts/clusters/agents/components/token_table.vue

@@ -18,7 +18,7 @@ export default {
     createToken: s__('ClusterAgents|You will need to create a token to connect to your agent'),
     dateCreated: s__('ClusterAgents|Date created'),
     description: s__('ClusterAgents|Description'),
-    lastUsed: s__('ClusterAgents|Last used'),
+    lastUsed: s__('ClusterAgents|Last contact'),
     learnMore: s__('ClusterAgents|Learn how to create an agent access token'),
     name: s__('ClusterAgents|Name'),
     neverUsed: s__('ClusterAgents|Never'),