contrib/database/sql: use tracer-level tags on contrib's statsd.Client

[mtoffl01]

What does this PR do?

The "DB Stats" metrics reported by the database/sql integration now accurately report hostname, env, lang and lang_version tags that were previously private to the tracer.
The tracer now publishes these tags so that integrations that submit statsd payloads (currently only database/sql) can use them.
The metrics also report the service tag, which is unique to the contrib. The service tag should not be shared from tracer to contribs, as contribs determine their own service name.

Motivation

Tags such as service and env are critical for correlating data across Datadog products (e.g, Metrics and APM), so it was important that these tags report accurately on our metrics.
Ref: https://docs.datadoghq.com/getting_started/tagging/unified_service_tagging/

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-04-03 15:10:14

Comparing candidate commit c840589 in PR branch mtoff/AIT-10026 with baseline commit 055b896 in branch main.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 43 metrics, 0 unstable metrics.

scenario:BenchmarkPartialFlushing/Enabled-24

• 🟩 execution_time [-11.879ms; -9.253ms] or [-4.171%; -3.249%]

[darccio]

@mtoffl01 Should we merge this?