Fixes #38015 - Handle empty content counts on Proxy UI

[pavanshekar]

What are the changes introduced in this pull request?

Updated the SmartProxyExpandableTable component to use optional chaining for safer property access and added a test case to validate correct behavior and UI rendering.

Considerations taken when implementing this change?

Ensured the component handles content_counts as an empty object {} without errors, maintains backward compatibility, and preserves UI consistency with appropriate placeholders for missing data.

What are the testing steps for this pull request?

Set content_counts = {}:

1. Got to Rails Console:
   bundle exec rails console
2. Assign Empty Object {} to the respective SmartProxy's content_counts attribute:
   sp = SmartProxy.find(smartproxy_id)
   sp.content_counts = {}
3. Save the changes:
   sp.save

Check the UI

1. Go to Infrastructure -> Smart Proxies -> Any Proxy -> Content
2. Expand Env -> Expand Content View
3. It should not give console error and able to view the fields with the value "N/A" for Packages and Additional Content

[sjha4]

Ack 👍🏼