Support Amazon Aurora DSQL as a connectable database

Is your feature request related to a problem?

Bytebase can't currently connect to Amazon Aurora DSQL. DSQL speaks the PostgreSQL wire protocol, so it would be natural to manage it as a Postgres-type instance, but two DSQL-specific requirements block the connection today:

1. SNI is required. Aurora DSQL routes by hostname and rejects TLS handshakes whose ClientHello carries no SNI. On Bytebase's password/SSL path, util.GetTLSConfig builds a tls.Config without ServerName, so no SNI is sent and the handshake is refused.
2. DSQL needs its own IAM auth token. DSQL does not support password auth; it requires an IAM token signed for the dsql:DbConnectAdmin / dsql:DbConnect actions via aws-sdk-go-v2/feature/dsql/auth. This differs from the RDS/Aurora token produced by feature/rds/auth, which Bytebase uses today, so there is no way to authenticate to DSQL.

Describe the solution you'd like

Allow Bytebase to connect to Aurora DSQL endpoints as a PostgreSQL-compatible instance:

• Send SNI (ServerName) on the PostgreSQL TLS path so DSQL accepts the handshake (skipping literal IPs per RFC 6066).
• On the AWS IAM authentication path, detect DSQL cluster endpoints (.dsql..on.aws) and sign the correct DSQL token — using the admin variant (dsql:DbConnectAdmin) for the built-in admin role and the regular variant (dsql:DbConnect) for custom database roles. The token is signed against the cluster endpoint hostname.
• Avoid sending session/startup parameters DSQL rejects (e.g. default_transaction_read_only), which would otherwise fail read-only connections (read-only data sources, data export).

Configuration would reuse the existing AWS RDS IAM authentication type and AWS credentials — no new UI option — with DSQL auto-detected from the endpoint.

Additional context

• Aurora DSQL PostgreSQL compatibility / supported session parameters: https://docs.aws.amazon.com/aurora-dsql/latest/userguide/accessing.html
• DSQL authentication token: https://docs.aws.amazon.com/aurora-dsql/latest/userguide/SECTION_authentication-token.html
• Implementation in progress: #20646
• Known limitation to track separately: AWS IAM tokens (RDS and DSQL) are currently baked in as a static password and not refreshed per connection, so connections opened after token expiry fail — a pre-existing issue shared with the RDS IAM path.