Add syslog filter test

[jorbaum]

What is this change about?

A new feature has been added to the syslog-agent of the loggregator-agent-release. This adds some initial tests to make sure users can use the feature as expected.

Please provide contextual information.

PR: cloudfoundry/loggregator-agent-release#714

Issue: cloudfoundry/loggregator-agent-release#711

Documentation PRs:

• Document new log-source-type syslog drain config docs-dev-guide#576
• Document more source types docs-dev-guide#577
• Improve log type filter docs-dev-guide#584

What version of cf-deployment have you run this cf-acceptance-test change against?

I deployed CF-on-K8s using cloudfoundry/kind-deployment at commit 3013ff1 (v0.20.0-16-g3013ff1).

Please check all that apply for this PR:

• introduces a new test --- Are you sure everyone should be running this test?
• changes an existing test
• requires an update to a CATs integration-config

Did you update the README as appropriate for this change?

• YES
• N/A

If you are introducing a new acceptance test, what is your rationale for including it CATs rather than your own acceptance test suite?

This is a new feature for syslog drains.

How many more (or fewer) seconds of runtime will this change introduce to CATs?

On my machine tests run through (including skipping tests) in roughly 8 minutes:

CONFIG="$HOME/Workspace/public/cloudfoundry/kind-deployment/.github/cats-config.json" go run github.com/onsi/ginkgo/v2/ginkgo --no-color --timeout=40m \
  --focus="Syslog Drain source type filter over TCP" .
  ...
Ran 2 of 288 Specs in 488.621 seconds

What is the level of urgency for publishing this change?

• Urgent - unblocks current or future work
• Slightly Less than Urgent

Tag your pair, your PM, and/or team!

@beyhan

Disclaimer: Claude Opus 4.8 (and Claude Code) generated this code, I reviewed carefully and edited.