Handle null issue_date for final opinion document and legal search results

[patphongs]

Summary

• Resolves AO does not load when issue_date is empty #6601

Handle null issue_date for final opinion document and legal search results table

Required reviewers

1 front end engineer

Impacted areas of the application

General components of the application that this PR will affect:

• Advisory opinions search results table
• Advisory opinions individual page

Screenshots

Related PRs

branch	PR
feature/6487-update-final-opinion-date	link

How to test

• Pull down this PR
• Hook up your local API to the dev environment as we've reproduced the error there
• Load the advisory opinions search page and ensure the issue date for AO 2024-15 has a blank issue date column
• Load the AO 2024-15 page and ensure page still loads with the final opinion document with a blank date and no date shown next to the advisory opinions button.