chore(docs): developer docs on plugin system communication

[j-lanson]

To start the hipcheck developer docs, I added a document and accompanying graphic explaining how Hipcheck core queries are conducted over gRPC.

@alilleybrinker I could use advice on where the .png / .drawio files should be stored in the site. I also need to set up to do local site dev to wire up this Markdown file to read the .png and be part of the Contributing page links.

@devin-b-lake @aamohd @ninaagrawal as the newer members on the team, I would appreciate if you read through the document and the graphic, and pointed out anything that was particularly confusing. The expectation is that someone would read it while looking through the functions it references.

[aamohd]

This is a little confusing. There's explanation for why and functionality for there being multiple Sender instances (if I'm understanding correctly), but I'm a little confused on how the HcSessionSocket is handling the situation. Is it that the HcSessionSocket forwards the session to the Receiver when it's free? And I might be misunderstanding the wording, but is the session within the send messages as a PluginEngine instance?

[j-lanson]

We don't send "sessions," we send "messages". A session is made up of a series of messages with the same ID. The HcSessionSocket forwards a message it receives on the Receiver tied to the gRPC channel, and then forwards it on one of the many Senders it has to different PluginEngine instances. I will add a graphic and update the explanation.

[j-lanson]

Added a graphic and expanded the description. @aamohd let me know if this is more clear.

[aamohd]

I left comments on plugin-query-system.md

[alilleybrinker]

Regarding where to put images, here's the guide from the Zola docs on "asset colocation": https://www.getzola.org/documentation/content/overview/#asset-colocation

The basic idea is that you turn the relevant page into a folder with an index.md file in it, and with the images you want to include on the page inside of that folder.

[alilleybrinker]

This page is one that we'll want to make sure we keep up-to-date. In general, I think we probably ought to add a review checklist for approvals on PRs, which would include a documentation review to make sure documentation is updated to reflect PR changes.

[j-lanson]

I added a PR Review Checklist page under the Contributing section. Let me know if you have any suggested changes.

[j-lanson]

Regarding where to put images, here's the guide from the Zola docs on "asset colocation": https://www.getzola.org/documentation/content/overview/#asset-colocation

The basic idea is that you turn the relevant page into a folder with an index.md file in it, and with the images you want to include on the page inside of that folder.

@alilleybrinker this doesn't actually show how to display co-located images in a markdown file. The way I found to work with a custom shortcut only works if the images are in static/