fix: resolve missing dependencies for Windows Kafka SASL support

[patrick-stephens]

Resolves #14 using techniques from fluent/fluent-bit#11294 although with some fixes.

---

Summary by cubic

Fix Windows Kafka SASL setup by enabling SASL via TLS instead of libsasl2 and failing misconfigured builds. Addresses #14 and prevents hidden dependency issues while aligning with librdkafka behavior on Windows.

• Bug Fixes
  • On Windows, enable SASL when TLS (FLB_TLS) is on; warn if TLS is off.
  • Keep libsasl2 detection via pkg-config and fallback for non-Windows builds.
  • Fail the build if Kafka SASL or OAuth Bearer is disabled (FATAL_ERROR).

^{Written for commit 03ecde1. Summary will update automatically on new commits.}

[patrick-stephens]

@cubic-dev-ai please review.

[cubic-dev-ai]

@cubic-dev-ai please review.

@patrick-stephens I have started the AI code review. It will take a few minutes to complete.

[cubic-dev-ai]

1 issue found across 1 file

Prompt for AI agents (all 1 issue)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="source/cmake/kafka.cmake">

<violation number="1" location="source/cmake/kafka.cmake:12">
P1: Rule violated: **Ensure tests are added**

Production code modified without corresponding test changes. The rule requires that changes to production files under `source/` (like `source/cmake/kafka.cmake`) include at least one test file change under `source/tests/` or `source/testing/`. Consider updating `source/tests/runtime/out_kafka.c` or adding a new CMake test to verify:
- Windows SASL enablement when FLB_TLS is on
- FATAL_ERROR behavior when SASL/OAuth Bearer is disabled</violation>
</file>

_{Reply to cubic to teach it or ask questions. Re-run a review with @cubic-dev-ai review this PR}

[coveralls]

coverage: 56.273%. remained the same
when pulling 03ecde1 on 14_oauth_support_windwos
into dedf52e on main.

[coveralls]

coverage: 56.272% (-0.001%) from 56.273%
when pulling 8bac230 on 14_oauth_support_windwos
into dedf52e on main.