chore(config): migrate ciVisibilityAgentless

[mtoffl01]

What does this PR do?

Migrates tracer to using Config.ciVisibilityAgentlessEnabled rather than its own config.ciVisibilityAgentlessEnabled

Motivation

datadoghq.atlassian.net/browse/APMAPI-1748

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.
• New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
• 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: 2025-12-10 17:24:25

Comparing candidate commit 1b718dc in PR branch mtoff/ciVisibilityAgentless with baseline commit 744a237 in branch mtoff/ciVisibilityEnabled.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.

[codecov]

Codecov Report

❌ Patch coverage is 21.42857% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.35%. Comparing base (744a237) to head (1b718dc).

Files with missing lines	Patch %	Lines
internal/config/config.go	0.00%	10 Missing ⚠️
ddtrace/tracer/tracer.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
ddtrace/tracer/civisibility_transport.go	60.00% <100.00%> (ø)
ddtrace/tracer/option.go	85.45% <100.00%> (+0.12%)	⬆️
ddtrace/tracer/telemetry.go	87.50% <100.00%> (ø)
ddtrace/tracer/tracer.go	86.40% <0.00%> (ø)
internal/config/config.go	62.82% <0.00%> (-8.20%)	⬇️

... and 5 files with indirect coverage changes

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