Add bkardell's Mastodon link (#3801)

* Update contributors.json

* Update src/config/contributors.json

* Nit - sorted order

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Co-authored-by: Barry Pollard <barrypollard@google.com>

Author: bkardell

src/config/contributors.json

@@ -719,6 +719,7 @@
   "bkardell": {
     "avatar_url": "870501",
     "github": "bkardell",
+    "mastodon": "https://toot.cafe/@bkardell",
     "name": "Brian Kardell",
     "teams": {
       "2019": [