Allow plugins to add tasks

[GerkinDev]

Feature description

Give the ability to plugins to mutate tasks list.

Motivating example

I'm using the 0.17.0-rc.0. From discussion in #548, I'm trying to move my logic to the plugin system. However, for ease of use, the plugin would need to setup itself in the graphile worker during bootstrap by adding its own internal tasks.

This would allow to remove any core logic specific for LoadTaskFromJsPlugin & LoadTaskFromExecutableFilePlugin.

This issue is not blocking, since my plugin factory could return the plugin and a task list, like so:

const pluginConfig = MyPlugin(someConfiguration)
await run({
    preset: { plugins: [pluginConfig.plugin] },
    taskList: {...pluginConfig.taskList}
}),

However it's easy to miss, and I think that allowing plugins to add their own tasks make sense

Supporting development

I [tick all that apply]:

• am interested in building this feature myself
• am interested in collaborating on building this feature
• am willing to help testing this feature before it's released
• am willing to write a test-driven test suite for this feature (before it exists)
• am a Graphile sponsor ❤️
• have an active support or consultancy contract with Graphile

[benjie]

Entirely reasonable. Here's the groundwork for it:

https://github.com/graphile/worker/compare/getTasks

Please raise a PR branched off of that that adds tests, and ensure it can accomplish what you need. And add some docs :)

Note that we are moving away from using hooks to using middleware now. Middleware are more powerful because they allow before/after actions. In this case you can straight up choose to not call the underlying function at all, thus never reading any tasks from the file system, should you so desire.

Oh, please also upgrade to the latest version of graphile-config@beta (if it has changed).