hackathon: Nail ~plugin docs~ apps

[jamesefhawkins]

Changes

Nails plugin docs

[joethreepwood]

This should be content complete now, in most major ways. It's a very big PR which:

• Gives each app a product page
• Gives each app a separate docs page
• Updates all docs and content to (mostly) refer to plugins as apps

Parallel to this I've already made changes to the contribution guidelines, so that new apps will be contributed with better documentation. Tutorials, which were previously a part of this PR, have already been split out and released too.

Following discussion in PostHog/posthog#9654 I've removed the built-in apps (funnels, trends) from the scope of this and left them as product features. However, there may be additional tidying up here for the Website team based on on-going product page work and apps directory work.

We should also sync deployment of this with the change of plugins to apps in the product and the release of Emanuele's new apps.

However, most of the words are now in and all the content actions from the initial checklist are also handled.

Milestone reached. Open to feedback.

[corywatilo]

@smallbrownbike I reverted 6ee8cfb as it was throwing an error on a fresh build. (We didn't notice because it wouldn't happen until a new build was triggered.)

internal/modules/cjs/loader.js:1089
      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
      ^

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /Users/cw/working/posthog.com/node_modules/gatsby-recipes/node_modules/remark-mdx/index.js
require() of ES modules is not supported.
require() of /Users/cw/working/posthog.com/node_modules/gatsby-recipes/node_modules/remark-mdx/index.js from
/Users/cw/working/posthog.com/node_modules/gatsby-recipes/dist/graphql-server/server.js is an ES module file as it is a .js file whose nearest parent package.json contains
"type": "module" which defines all .js files in that package scope as ES modules.
Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from
/Users/cw/working/posthog.com/node_modules/gatsby-recipes/node_modules/remark-mdx/package.json.

from build logs:

7:09:07 PM: error "gatsby-node.js" threw an error while running the createPages lifecycle:
7:09:07 PM: Syntax Error: Expected Name, found )
7:09:07 PM: 
7:09:07 PM: 
7:09:07 PM:   GraphQLError: Syntax Error: Expected Name, found )
7:09:07 PM: 
7:09:07 PM: failed createPages - 0.025s

Edit: Since we're keeping product pages inside /product, I realized we can just move the mdx files back into the /product directory since they're the same as what were moved into /apps so this commit isn't needed anymore. Safe to ignore!

[corywatilo]

yolo