migrate to pyproject.toml

[rinarakaki]

This is the tracking issue for googleapis's pyproject.toml support.

List

• feat: migrate to pyproject.toml google-auth-library-python#1607
• feat: migrate to pyproject.toml python-api-core#736
• feat: migrate to pyproject.toml python-cloud-core#304
• feat: migrate to pyproject.toml python-grpc-google-iam-v1#112
• feat: migrate to pyproject.toml proto-plus-python#496
• feat: migrate to pyproject.toml google-resumable-media-python#456
• feat: migrate to pyproject.toml python-api-common-protos#255
• AI Platform feat: migrate to pyproject.toml python-aiplatform#4549
• Audit Log feat: migrate to pyproject.toml python-audit-log#153
• BigQuery feat: migrate to pyproject.toml python-bigquery#2041
• DNS feat: migrate to pyproject.toml python-dns#290
• Logging feat: migrate to pyproject.toml python-logging#949
• Pub/Sub feat: migrate to pyproject.toml python-pubsub#1277
• Spanner feat: migrate to pyproject.toml python-spanner#1211
• Storage feat: migrate to pyproject.toml python-storage#1364

Closes #10528.