sql_insert doesn't support bloblang interpolation in dsn field

Hi,

Is there a way to support interpolation in dsn field in sql_insert?
Our usecase: we read messages as inputs, we want to use AWS IAM role based authentication to postgres on RDS. So dsn will have password as token generated by aws.

There can be other usecases like based on metadata of message we want to route message to different DB server host.

I can see code in
https://github.com/redpanda-data/connect/blob/main/internal/impl/sql/conn_fields.go#L33
https://github.com/redpanda-data/connect/blob/main/internal/impl/sql/output_sql_insert.go#L38C9-L38C17
dsnField is not defined as NewBloblangField like arg_mapping or topics for input here.

Purposed solutions (either of below):

1. we can change dsnField to NewBloblangField
2. add support for IAM based authentication which will use golang aws sdk to get token and use that instead of password in sql_insert output.

output:
  sql_insert:
    driver: postgres
    dsn: 'postgres://postgres:${! meta("pg_pass") }@localhost:5432/postgres?sslmode=disable'
    table: test
    iam_based_auth:
          role: 'somerole_aws_role' 
          ....

My test config:

inputs:
  label: ""
  redpanda:
    seed_brokers: [] # No default (optional)
    topics: [] # No default (required)
    regexp_topics: false
    transaction_isolation_level: read_uncommitted
    consumer_group: "" # No default (optional)
    auto_replay_nacks: true
pipeline:
  processors:
    - mapping: |
#        we need to get this from message metadata or our dynamic plugin which will generate password for given message
#        metadata which will replace pg_pass here.
        meta pg_pass = "postgres" 
output:
  sql_insert:
    init_statement: | # No default (optional)
      CREATE TABLE IF NOT EXISTS test (
           alias VARCHAR,
           query VARCHAR not null,
           parsing_time BIGINT);
    driver: postgres
    dsn: 'postgres://postgres:${! meta("pg_pass") }@localhost:5432/postgres?sslmode=disable'
    table: test
    columns:
      [
        "alias",
        "query",
        "parsing_time"
      ]
    args_mapping: root = [
      this.alias,
      this.query,
      this.parsing_time ]
    max_in_flight: 64

Read internal/impl/sql/conn_fields.go and internal/impl/sql/output_sql_insert.go, focusing on dsnField and the existing Bloblang fields. Reproduce the provided sql_insert configuration with a metadata-generated password, then review the relevant SQL output tests. Done means the selected approach supports the requested dynamic DSN use case and has coverage for it.