chore: update mqtt to latest 5.x and remove unneeded async-mqtt wrapper

[sorccu]

It seems that the async-mqtt wrapper has not been updated for a few years and our usage does not require it. It's more future proof to just use mqtt directly.

Relevant MqttClient calls have been updated to Async variants.

I hereby confirm that I followed the code guidelines found at engineering guidelines

Affected Components

• CLI
• Create CLI
• Test
• Docs
• Examples
• Other

Notes for the Reviewer

Resolves #[issue-number]

New Dependency Submission

While technically mqtt was added to package.json, it was already used indirectly via async-mqtt.

[clample]

We can drop async-mqtt if you think it's the way to go, but I think the subscribe() call needs to be updated:

checkly-cli/packages/cli/src/services/abstract-check-runner.ts

Line 127 in 5dbec8c

await socketClient.subscribe(`account/${this.accountId}/ad-hoc-check-results/${checkRunSuiteId}/+/+/+`)

If we switch to the main mqtt client, I think this will no longer return a promise (it will use a callback), so this will not block until the client is subscribed to the topic. We should be careful with this one, since the client needs to subscribe to the topic before the check runs are triggered. Otherwise, there's a bit of room for a race condition - the client triggers checks but misses the results.

Also I think end() will go from returning a promise to using a callback. This one is less important, though.

checkly-cli/packages/cli/src/services/abstract-check-runner.ts

Line 112 in 5dbec8c

await socketClient.end()

[clample]

Looks good!