Update developer documentation from Jitsu to Snowplow event collection

What does this MR do and why?

This MR updates the project settings controller to pass along the :product_analytics_snowplow_support feature flag as it needs to render different content based upon whether this flag is enabled.

I also took the time to add a small paragraph to direct users to the browser SDK documentation if they want to see what other options are available.

Screenshots or screen recordings

With the flag disabled

Onboarding view

Before	After

Project settings view

Before	After

With the flag enabled

Onboarding view

Before	After

Project settings view

Before	After

How to set up and validate locally

1. Follow these instructions to set up Product Analytics in your GDK.
   • Make sure to set up both the Jitsu and Snowplow related fields.
2. Set up a new project and start setting it up via Project → Analytics → Dashboards.
3. Confirm the instrumentation details are for Jitsu.
4. Track some events and page views for the project via the SDK.
5. Visit the projects settings via Project → Settings → General → Product Analytics.
6. Confirm the instrumentation details are for Jitsu.
7. Enable the Snowplow flag by running the command: echo "Feature.enable(:product_analytics_snowplow_support)" | rails c.
8. Repeat steps 2. → 6 but for Snowplow details instead.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #405145 (closed)