feat(iast): iast telemetry metrics base

[avara1986]

Implement executed.source metric

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment.
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[pr-commenter]

Benchmarks

Comparing candidate commit dc82cd6 in PR branch avara1986/APPSEC-10269-iast_metrics with baseline commit a346cdd in branch 1.x.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 92 cases.

scenario:flasksimple-appsec-get

• 🟩 execution_time [-0.328ms; -0.289ms] or [-5.194%; -4.583%]

scenario:flasksimple-appsec-telemetry

• 🟩 execution_time [-0.340ms; -0.299ms] or [-5.363%; -4.709%]