Opentelemetry-java: Semantic constants for db.system

[trask]

Does it make sense have semantic constants somewhere for db.system? based on the spec table https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/semantic_conventions/database.md

| Value | Description |
|---|---|
| other_sql | Some other SQL database. Fallback only. See notes. |
| mssql | Microsoft SQL Server |
| mysql | MySQL |
| oracle | Oracle Database |
| db2 | IBM Db2 |
| postgresql | PostgreSQL |
| redshift | Amazon Redshift |
| hive | Apache Hive |
| cloudscape | Cloudscape |
| hsqlsb | HyperSQL DataBase |
| progress | Progress Database |
| maxdb | SAP MaxDB |
| hanadb | SAP HANA |
| ingres | Ingres |
| firstsql | FirstSQL |
| edb | EnterpriseDB |
| cache | InterSystems Caché |
| adabas | Adabas (Adaptable Database System) |
| firebird | Firebird |
| derby | Apache Derby |
| filemaker | FileMaker |
| informix | Informix |
| instantdb | InstantDB |
| interbase | InterBase |
| mariadb | MariaDB |
| netezza | Netezza |
| pervasive | Pervasive PSQL |
| pointbase | PointBase |
| sqlite | SQLite |
| sybase | Sybase |
| teradata | Teradata |
| vertica | Vertica |
| h2 | H2 |
| coldfusion | ColdFusion IMQ |
| cassandra | Apache Cassandra |
| hbase | Apache HBase |
| mongodb | MongoDB |
| redis | Redis |
| couchbase | Couchbase |
| couchdb | CouchDB |
| cosmosdb | Microsoft Azure Cosmos DB |
| dynamodb | Amazon DynamoDB |
| neo4j | Neo4j |

[thisthat]

I'll propose a way to generate them automatically from the YAML definitions :)