UI polish for Related Issues

Discussed in call with @jschatz1 @victorwu

• Use ... for badge number before we actually know a number
• Focus input on form expansion
• Enable submit button when text is in input
• Update generic submission error message: "We can't find an issue that matches what you are looking for"
• Get rid of "Add an issue" tooltip on badge
• Get rid of "Remove issue" x icon tooltip on badge
• Update submit button text to simply "Add"
• Change placeholder to "Paste issue link or <#issue id>"