Add MQTT trigger and tests

[kate-goldenring]

closes #111

This should be merged first and then ideally a release of the trigger cut: spinkube/spin-trigger-mqtt#29

Adds an MQTT test which contains a deployment for an MQTT broker and a spin app that is triggered by the the broker.

[kate-goldenring]

@Mossaka have you seen these build errors before?

[devigned]

Looks like it's failing trying to find OpenSSL:

  -- The C compiler identification is GNU 9.2.0
  -- Detecting C compiler ABI info
  -- Detecting C compiler ABI info - done
  -- Check for working C compiler: /usr/local/bin/x86_64-linux-musl-gcc - skipped
  -- Detecting C compile features
  -- Detecting C compile features - done
  -- CMake version: 3.23.1
  -- CMake system name: Linux
  -- Timestamp is 2024-07-31T18:11:49Z
  -- Configuring incomplete, errors occurred!
  See also "/target/x86_64-unknown-linux-musl/release/build/paho-mqtt-sys-2d67149a03469667/out/build/CMakeFiles/CMakeOutput.log".

  --- stderr
  fatal: not a git repository (or any parent up to mount point /home/runner)
  Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
  CMake Error at /usr/local/share/cmake-3.23/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
    Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the
    system variable OPENSSL_ROOT_DIR (missing: OPENSSL_CRYPTO_LIBRARY
    OPENSSL_INCLUDE_DIR)
  Call Stack (most recent call first):
    /usr/local/share/cmake-3.23/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
    /usr/local/share/cmake-3.23/Modules/FindOpenSSL.cmake:578 (find_package_handle_standard_args)
    src/CMakeLists.txt:194 (find_package)


  thread 'main' panicked at /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/cmake-0.1.50/src/lib.rs:1098:5:

  command did not execute successfully, got: exit status: 1

[kate-goldenring]

@devigned yeah it has to do with how the paho-mqtt lib pulls in openssl. I am adding in their workaroud now: https://github.com/eclipse/paho.mqtt.rust?tab=readme-ov-file#fully-static-builds-with-musl

[rajatjindal]

we had similar issue in Spin when adding MQTT support, and static builds were fixed using this PR: https://github.com/fermyon/spin/pull/2307/files

could we please see if that fix helps in this case here. unfortunately the CI logs for that PR are gone, so can't really verify the exact error msg.

[kate-goldenring]

@rajatjindal thank you! that got me past the build errors.

[radu-matei]

Once CI is happy, LGTM.

Thank you!

[kate-goldenring]

After many iterations on the e2e test configuration we are all green 🎉
@devigned @Mossaka @jsturtevant this is ready for a final review

[devigned]

lgtm!