splunksql: Add splunksql.OpenDB function

[pellared]

Add splunksql.OpenDB function for ones who dislike the sql.Open and splunksql.Open which use global state.

Something similar to https://pkg.go.dev/github.com/XSAM/otelsql#OpenDB

Desired API: func OpenDB(c driver.Connector, cfg InstrumentationConfig) *sql.DB.
We should also add OpenDB functions to all other sql-based instrumentation libraries that will use splunksql.OpenDB.

Implementation guidelines: #88 (comment)

Originally posted by @pellared in #88 (comment)

[pellared]

Waiting until anyone asks for this feature.

[joshi-kamitsukasa]

Hi, we want splunksql.OpenDB function. We want to use pgx Connector's option (e.g. OptionAfterConnect) but we can't use it with splunksql.

[pellared]

@joshi-kamitsukasa Could you please add a snippet how would you use such function?

My guess is that it would rather prefer using func OpenDB(config pgx.ConnConfig, opts ...stdlib.OptionOpenDB) *sql.DB that could be added to https://pkg.go.dev/github.com/signalfx/splunk-otel-go/instrumentation/github.com/jackc/pgx/v5/splunkpgx.

Of course we would need to create splunksql.OpenDB anyway 😉

If you would like to have this sooner rather than later, please contact Splunk's support/sales to escalate this issue. More: https://docs.splunk.com/observability/en/get-started/support.html

[joshi-kamitsukasa]

@pellared Thanks for your reply.

For example below,

	return stdlib.OpenDB(*pgxConfig, []stdlib.OptionOpenDB{
		stdlib.OptionAfterConnect(func(ctx context.Context, conn *pgx.Conn) error {
			pgxdecimal.Register(conn.TypeMap())
			return setXxxxxFunc(ctx, conn)
		}),
		stdlib.OptionResetSession(setXxxxxFunc),
	}...), nil

We are going to contact support. Thanks.