Add scaling information for Cloud users

[ptgott]

Details

Currently, our Scaling guide focuses on the Auth Service and Proxy Service. We should add information that benefits Cloud users, such as:

• How much the managed Auth Service and Proxy Service scale in relation to a tenant's connected agents
• If it's possible to request more compute/storage capacity for a cloud tenant
• If there are any vertical scaling recommendations for a single agent host (e.g., one teleport binary configured to access a server, database, etc.)

We can consider adding a separate page for this.

Category

• Improve Existing

[alexfornuto]

While we're working on this page, we should expand this page to not just discuss SSH nodes, but DB/Desktop access and anything else we provide secured access to. This could also be spun into a separate issue, if we determine the scope is to large.

[ptgott]

Addressed in #38178