.github: add Blunderbuss config
.github: add Blunderbuss config

This will make it so issues with the corresponding label will automatically
be assigned to a random user listed for that label.

Change-Id: Ica2d3a95dbdd25cfa1cb465edc6bdbdc17ca631c
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/57190
Reviewed-by: Seth Hollyman <10194de3bbef2536f4b5d02c780e8788d90cab2e@google.com>
Reviewed-by: Chris Cotter <b879ae7d4b52f11ce9f60d9854075eb8eebaf7a9@google.com>
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Cody Oss <f11fa1e55ff5638510f5bf86ea76672a630250f9@google.com>
Reviewed-by: Shanika Kuruppu <382bd9679e6cb7e2135c45a8cd1be9e02cd75f23@google.com>
Reviewed-by: Alex Hong <3311379d571f0e1dc66d44c9732cbfa024b0fda6@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go