PRICING page - Allow plan to be picked based on query param

[smallbrownbike]

Changes

• Sets the initial plan on the pricing page based on the plan query parameter in the URL
• Updates links to support new query parameter

Options are:

• cloud
• cloud-enterprise
• self-hosted
• self-hosted-enterprise

Example: https://posthog.com/pricing?plan=cloud-enterprise

[jamesefhawkins]

(this isn't a blocker but we need to figure out if we're already passing parameters like this that are now broken, for the previous plans page)

[pjhul]

Did a quick search and it seems as though the only places we used the realm parameter were in the FeatureAvailability component which Eli already updated :+1:

[smallbrownbike]

@jamesefhawkins I’m not sure if any external links are using “realm” but I updated this PR to support both “realm” and “plan” just in case!

[joethreepwood]

This seems outdated, so 🔐