contrib/database/sql: allow peer.service to be set explicitly and add into propagated context

[tabgok]

What does this PR do?

This PR does two things:

1. Adds peer.service to the SQL Connection context if set explicitly by a user via the Traced Connector Context or tag
2. Adds ddprs=peer.service to the SQL Comment propagation when full mode is enabled

Motivation

This change allows the DBM and APM service maps to line up

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.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-05-22 14:35:14

Comparing candidate commit 26753a3 in PR branch teague.bick/AIT-10033/dbm-peer-entity with baseline commit 14d15d5 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 47 metrics, 0 unstable metrics.

[tabgok]

/merge

[dd-devflow]

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[darccio]

@tabgok I'll handle the merge.