Make docker builds less verbose (#11564) (#11599)

We producess 100Mb+ of logs for each container build currently, because
buildkit believes it's running in an interactive tty.

(cherry picked from commit 23c82ae)

Co-authored-by: Mikołaj Świątek <[email protected]>

Author: mergify[bot]

.buildkite/integration.pipeline.yml

@@ -4,6 +4,9 @@ env:
   VAULT_PATH: "kv/ci-shared/observability-ingest/cloud/gcp"
   ASDF_MAGE_VERSION: 1.14.0
 
+  # Make Docker builds less verbose
+  BUILDKIT_PROGRESS: plain
+
   # The following images are defined here and their values will be updated by updatecli
   # Please do not change them manually.
   IMAGE_UBUNTU_2204_X86_64: "platform-ingest-elastic-agent-ubuntu-2204-1764775167"