Add instrumentation for the database/sql package

[MrAlias]

This new module instruments the built-indatabase/sql package. The instrumentation wraps all calls made with this package and is designed with a similar registration method for instrumentation setup (more on that bellow).

• Comply with OpenTelemetry database semantic conventions
• Package documentation
• Exported objects are documented
• Tests and linting are passing
• Includes dependabot config
• Library added to README.md

Instrumentation of specific drivers

The design of the splunksql package is such that users wanting an instrumented version of their driver and the database/sql package need to do two things.

1. Update their import of the driver they are using to the instrumented driver.
2. Use the splunksql.Open function instead of the sql.Open function.

To understand this flow, take for instance the generic example of a user using the MySQL driver with the database/sql package. To start their code looks like this.

import (
	"database/sql"

	_ "github.com/go-sql-driver/mysql"
)

// ...

db, err := sql.Open("mysql", "user:password@/dbname")
// ...

To use this instrumentation, their code will need to be updated to this.

import (
	"database/sql"

	_ "github.com/signalfx/splunk-otel-go/instrumentation/github.com/go-sql-driver/mysql/splunkmysql"
	"github.com/signalfx/splunk-otel-go/instrumentation/database/sql/splunksql"
)

// ...

db, err := splunksql.Open("mysql", "user:password@/dbname")
// ...

The import of github.com/signalfx/splunk-otel-go/instrumentation/github.com/go-sql-driver/mysql/splunkmysql will import the instrumented github.com/go-sql-driver/mysql (registering its driver with the database/sql package) and itself register instrumentation specific setup with the splunksql package (e.g. this). Then when the user calls splunksql.Open (which is a drop in replacement for sql.Open based on its variadic Option design). the registered driver and instrumentation setup will be loaded appropriately. From this, telemetry that knows what database it is for and annotated according to the OpenTelemetry semantic conventions is produced.

The need to register instrumentation setup comes from the need to parse the database connection string. That string will contain needed annotations and the way it is parsed is going to be specific to the database being instrumented.

This registration method differed from the existing signalfx-go-tracing instrumentation. There the database/sql package is designed to hold all parsing logic. This is a design that will not extend well, unlike the one presented here.

Uninstrumented drivers

If the user does not import an instrumentation package for the driver they are using, or one does not exist, the splunksql.Open function can still be extended to accommodate this. The returned sql.DB will still use an instrumented Driver which will produce telemetry. If the user passes attributes conforming to OTel semantic conventions using the WithAttributes Option as a parameter the produced telemetry will comply with the OTel specification.

[pellared]

Do you want to add a splunksql/instrumentation/database/sql/splunksql/README.md in this PR or in another one? Moreover, I think it would be nice to add an example_test.go - I think it should demonstrate the "Uninstrumented drivers" scenario as examples for the instrumented ones could be in their respective directories.

Also, we need to think if we should not move this PR to https://github.com/open-telemetry/opentelemetry-go-contrib

Can this approach of instrumenting ng via otelsql.Open can live side-by-side with the approach of instrumenting via otelsql.Register proposed here
open-telemetry/opentelemetry-go-contrib#505?

[MrAlias]

Do you want to add a splunksql/instrumentation/database/sql/splunksql/README.md in this PR or in another one? Moreover, I think it would be nice to add an example_test.go - I think it should demonstrate the "Uninstrumented drivers" scenario as examples for the instrumented ones could be in their respective directories.

Yeah, let's do that in a follow on PR. This is quite large already.

[pellared]

An idea for the next PR with documentation.

I think it may be a good idea to demonstrate how to add an additional attribute like db.sql.table. Never done it but I believe it is possible to it via ctx.

[pellared]

LGTM

I guess your are finishing adding explanations to places with nolint: 😉