feat: [java] allow passing libraries_bom_version from env (#1967) (#6596)

* feat: [java] allow passing libraries_bom_version from env

* reformat
Source-Link: googleapis/synthtool@e36d2f1
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:31aa2ef27b071c2e7844b0eb1d5a24254daff06615b1b138b994dd6345c0b0ea

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,5 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:d13de1a4faec2645bda630b7a9aa080ce95182795aeab6f37ed4bd18cf5facbc
-# created: 2024-04-24T14:22:15.892514394Z
+  digest: sha256:31aa2ef27b071c2e7844b0eb1d5a24254daff06615b1b138b994dd6345c0b0ea
+# created: 2024-05-17T15:15:57.6714113Z