Fix: Prevent crashes when accessing cluster details

[am6737]

• Added optional chaining to safely access cluster details in AddClusterDialog.

This fix addresses the issue where the page crashes when trying to load details for an inaccessible cluster.

Description of your changes

Fixes #685

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run yarn lint to ensure the frontend changes are ready for review.
• Run make reviewableto ensure the server changes are ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

Special notes for your reviewer

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.08%. Comparing base (2ab672c) to head (5703b22).
Report is 4 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (2ab672c) and HEAD (5703b22). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (2ab672c)	HEAD (5703b22)
apiserver-unittests	1	0
server-e2e-tests	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #910      +/-   ##
==========================================
- Coverage   59.01%   51.08%   -7.94%     
==========================================
  Files         116      116              
  Lines       19846    16511    -3335     
==========================================
- Hits        11713     8434    -3279     
- Misses       6696     6846     +150     
+ Partials     1437     1231     -206     

Flag	Coverage Δ
apiserver-unittests	?
server-e2e-tests	51.08% <ø> (+2.76%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.