enhancement: improve bug report template

[fillwithjoy1]

First time contributor checklist

• I have read the README and CONTRIBUTING documents
• I have signed the Contributor Licence Agreement

Contributor checklist

• My commits are rebased on the latest main branch
• My commits are in nice logical chunks
• My contribution is fully baked and is ready to be merged as is
• I have tested my contribution on these devices:

• iDevice A, iOS X.Y.Z
• iDevice B, iOS Z.Y

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Description

This PR just adds a useful link to search all issues in the Signal iOS repo. The link doesn't have the "is:open" tag and just has the "is:issue" tag to include both open and closed issues