EDU-3229: Workflow Initializers Encyclopedia entry

[drewhoskins-temporal]

What does this PR do?

Overview documentation the new Workflow Initializer feature.

Notes to reviewers

• Per-SDK docs are TBD.
• Plan is to link to this from my blog post on message handling.

Test plan:

yarn start
http://localhost:3000/encyclopedia/workflow-message-passing#workflow-initializers

Click on links.

[fairlydurable]

@drewhoskins-temporal This is a wonderful expansion that reduces developer confusion and helps make sure that handlers aren't run before Workflow state is set.

Based on the Friday meeting, Docs/EDU should be providing guidance rather than re-writes. Happy to set up a Zoom call.

A few points of feedback

1. Tone: Aiming for a formal but friendly/supportive tone with few complex words and short sentences. For instance, the phrase "So, it's important to initialize your Workflow's state" can be revised to "Always initialize Workflow state before registering message handlers." It's more formal, it avoids passive voice, and it's more specific.
2. Context The start is abrupt. Spend a little more time introducing what's going on. A clear introduction explains the content purpose and importance. For example, start with a statement like, "Initializing Workflow state helps applications handle incoming messages correctly." (with your words of course.) This sets the stage for the discussion from the outset. Then, try to expand with motivation of what they'll get from this section. "Under normal circumstances, your messages might be processed before a Workflow's main method runs for the first time. You can see this in the Message Handler flow shown in the concurrency diagram on this page. In practice, this often happens in two scenarios:" (again, your words)
3. Construction: Avoid passive voice and minimize modal auxiliaries. If you have access to Open AI or similar, I can suggest some prompts that will tighten the text so you don't have to do it by hand, saving time. The other two points need planning and thought, but this one really doesn't.

Thank you for filing the ticket and getting this update underway. It's appreciated.

Also, always feel free to reach out to me to help me improve my feedback. As we're growing our cooperation I want to find ways to best support these items.

[fairlydurable]

Only because of previous tickets do I know that this really means something along the lines of blocking the Workflow's completion until all handlers have finished processing, otherwise I don't know if it really would be meaningful to me at first read.

Suggest minor rewording to make it clearer

[fairlydurable]

This is very cool. Whose responsibility is this? Is it worth a sidebar ("admonition"/callout) with a link to a source of truth to explain? Does this happen often?

[fairlydurable]

I think you mean that it prevents your Handlers from reading uninitialized instance variables.

Suggested change

	Initialize your Workflow's state before handling messages. This prevents your Workflow reading uninitialized instance variables.
	Initialize your Workflow's state before handling messages.
	This prevents your Handlers from reading uninitialized instance variables if they arrive before the Workflow state is entire set up.