fix(engine): reject empty appended rules

[Jvlegod]

What type of PR is this?

/kind bug

Any specific area of the project related to this PR?

/area engine

/area tests

What this PR does / why we need it:

This PR restores validation for append: true rules that do not actually append anything.

It also updates the related rule loader tests to cover:

• append: true with only enabled
• append: true without condition or exceptions

Which issue(s) this PR fixes:

N/A

Special notes for your reviewer:

Tested with:

cmake -S . -B build-agent -DMINIMAL_BUILD=On -DBUILD_DRIVER=Off -DBUILD_FALCO_UNIT_TESTS=On
cmake --build build-agent --target falco_unit_tests
sudo ./build-agent/unit_tests/falco_unit_tests

Does this PR introduce a user-facing change?:

NONE

[poiana]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Jvlegod
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[poiana]

Welcome @Jvlegod! It looks like this is your first PR to falcosecurity/falco 🎉

[github-actions]

This PR may bring feature or behavior changes in the Falco engine and may require the engine version to be bumped.

Please double check userspace/engine/falco_engine_version.h file. See versioning for FALCO_ENGINE_VERSION.

/hold

[Jvlegod]

Maybe I don't think FALCO_ENGINE_VERSION needs to be bumped.

[leogr]

This PR may bring feature or behavior changes in the Falco engine and may require the engine version to be bumped.

Please double check userspace/engine/falco_engine_version.h file. See versioning for FALCO_ENGINE_VERSION.

/hold

False positive
/hold cancel