feat: enable hermetic code generation

.github/workflows/hermetic_library_generation.yaml

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Generates the code changes that correspond to changes in generation_config.yaml.
+# A pull request is also created with these changes
+name: Hermetic library generation upon generation config change through pull requests
+on:
+  pull_request:
+  workflow_dispatch:
+jobs:
+  update-googleapis-commit:
+    uses: googleapis/sdk-platform-java/.github/workflows/hermetic_library_generation.yaml@centralized-hermetic-workflows
+

.github/workflows/update_googleapis_committish.yaml

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+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Updates the googleapis_committish entry in generation_config.yaml
+# The updated value is the commit hash of googleapis/googleapis@HEAD
+name: Update googleapis committish
+on:
+  schedule:
+  - cron: '* 2 * * *'
+  workflow_dispatch:
+jobs:
+  update-googleapis-commit:
+    uses: googleapis/sdk-platform-java/.github/workflows/update_googleapis_comittish.yaml@centralized-hermetic-workflows

generation_config.yaml

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+gapic_generator_version: 2.40.0
+protoc_version: '25.3'
+googleapis_commitish: 25a1a57957d9e4bf431897d280b2569b26dc9165
+libraries_bom_version: 26.38.0
+template_excludes:
+  - .gitignore
+  - .kokoro/presubmit/integration.cfg
+  - .kokoro/presubmit/graalvm-native.cfg
+  - .kokoro/presubmit/graalvm-native-17.cfg
+  - .kokoro/nightly/integration.cfg
+  - .kokoro/presubmit/samples.cfg
+  - .kokoro/nightly/samples.cfg
+  - .github/ISSUE_TEMPLATE/bug_report.md
+  - .github/PULL_REQUEST_TEMPLATE.md
+  - .github/trusted-contribution.yml
+  - CONTRIBUTING.md
+  - codecov.yaml
+  - .github/release-please.yml
+  - renovate.json
+  - .kokoro/requirements.in
+  - .kokoro/requirements.txt
+libraries:
+- api_shortname: bigtable
+  name_pretty: Cloud Bigtable
+  product_documentation: https://cloud.google.com/bigtable
+  client_documentation: https://cloud.google.com/java/docs/reference/google-cloud-bigtable/latest/history
+  issue_tracker: https://issuetracker.google.com/savedsearches/559777
+  release_level: stable
+  distribution_name: com.google.cloud:google-cloud-bigtable
+  codeowner_team: @googleapis/api-bigtable @googleapis/api-bigtable-partners
+  api_id: bigtable.googleapis.com
+  library_type: GAPIC_COMBO
+  extra_versioned_modules: google-cloud-bigtable-emulator,google-cloud-bigtable-emulator-core
+  excluded_poms: google-cloud-bigtable-bom
+  GAPICs:
+  - proto_path: google/bigtable/v2
+  - proto_path: google/bigtable/admin/v2