Consolidate bug labels (#24707)

Summary:
We currently have "Type: Bug Report", "Type: Bug Fix", and "Impact: Bug" in our list of labels. To simplify life for maintainers, lets use a single Bug label.

This PR makes it so new Bug Reports use the "Bug" label. The bot has been updated to accept "Bug" as a valid template label already.

[General] [Changed] - New issues use the Bug label
Pull Request resolved: https://github.com/facebook/react-native/pull/24707

Differential Revision: D15220772

Pulled By: hramos

fbshipit-source-id: e25f7180839d2e6aa7211b805dfbf5368b39d738

.github/ISSUE_TEMPLATE/bug_report.md

@@ -2,7 +2,7 @@
 name: "🐛 Bug Report"
 about: You want to report a reproducible bug or regression in React Native.
 title: ''
-labels: 'Type: Bug Report'
+labels: 'Bug'
 
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