[CI] Migrate CI pipelines from Jenkins to BuildKite (#8142)

* [CI] Migrate CI pipelines from Jenkins to BuildKite

* Require manual approval

* Less verbose output when pulling Docker

* Remove us-east-2 from metadata.py

* Add documentation

* Add missing underscore

* Add missing punctuation

* More specific instruction

* Better paragraph structure

tests/buildkite/build-jvm-doc.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source tests/buildkite/conftest.sh
+
+echo "--- Build JVM packages doc"
+tests/ci_build/ci_build.sh jvm docker tests/ci_build/build_jvm_doc.sh ${BRANCH_NAME}
+if [[ ($is_pull_request == 0) && ($is_release_branch == 1) ]]
+then
+  echo "--- Upload JVM packages doc"
+  aws s3 cp jvm-packages/${BRANCH_NAME}.tar.bz2 \
+    s3://xgboost-docs/${BRANCH_NAME}.tar.bz2 --acl public-read --no-progress
+fi