Tests for tcp.echo, tls.echo and http.kafka.sync examples

[attilakreiner]

This change introduces automated tests for tcp.echo, tls.echo and http.kafka.sync examples.

Fixes #125

[jfallows]

Is it necessary to repeat the failure output here when the test fails early?
In the general case, where it is possible to fail early in N different ways, this would be repeated N times.

For example, if each part is a function, then the execution invokes each function in turn, skipping over functions after early failure, falling through to output success or failure once.

[attilakreiner]

Actually my preference is to repeat those two lines (echo x; exit 1) whenever it makes sense to exit prematurely as opposed to introduce complex control flow with functions and such. This way we can keep a linear execution flow with the only exception of exiting early in case of fatal errors. I hope it's OK this way.

[jfallows]

Can we use apt package kafkacat instead of this manual install?

https://github.com/edenhill/kcat?tab=readme-ov-file#install

[attilakreiner]

The apt package kafkacat installs kafkacat version 1.6.0 that means it's lagging ca. one year behind the latest release. Even if we installed that we'd need to do some manual steps (e.g. renaming the executable from kafkacat to kcat) to keep the test in sync with the README and executable on other systems (e.g. on a Mac which has the latest kcat installed with brew).

[attilakreiner]

Actually I tested it, and that approach runs the test green, too. This is the alternative configuration:

      - name: Install apt packages
        uses: awalsh128/cache-apt-pkgs-action@latest
        with:
          packages: kafkacat
          version: 1.0
      - name: Setup kcat
        run: |
          sudo ln -s /usr/bin/kafkacat /usr/local/bin/kcat
          kcat 2>&1 | grep "Version 1.6.0"

Pls LMK which one you prefer.

[attilakreiner]

I reverted the apt install commit as discussed, so going back to manual installation of kcat, as the decision was to install the latest version.