A11Y: Add label to share link input (PR #10717)

This input needs to be labeled for screen readers, discussion here: https://meta.discourse.org/t/ramp-accessibility-issues/164000/7

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This pull request has been mentioned on Discourse Meta. There might be relevant details there:

https://meta.discourse.org/t/ramp-accessibility-issues/164000/8

The lint failure must be unrelated.