Improve Pulumi ESC Getting Started

[meagancojocar]

Problem description

Came up recently in a few 1:1s. Focus on how to use ESC with IaC instead of focusing on creating a Pulumi Account etc.

[VenelinMartinov]

1. Took me a bit of time to find them - we don't link that use case from the main landing page: https://www.pulumi.com/docs/esc/. Is this not one of the main use cases for ESC?
2. Looking at https://www.pulumi.com/docs/esc/get-started/integrate-with-pulumi-iac/:

• We spend two screens worth of docs explaining how IAC config works, which is unrelated to ESC. This feels unnecessary given that the audience for that page should be people who work with both.
• At the bottom of the page we have a paragraph about accessing config from ESC and pulumiConfig in ESC, which is good: https://www.pulumi.com/docs/esc/get-started/integrate-with-pulumi-iac/#access-configuration-from-esc but it kind of misses the point.
• Integrating IAC with ESC is as simple as adding the environment bit to your Pulumi.dev.yaml. That should be the main use case for most users - the ESC env is now available for the IAC program. We don't say that anywhere on that page.

[VenelinMartinov]

I think we should have a paragraph first about dropping environment in your Pulumi.dev.yaml and it "just works" - you can now access ESC env from IaC. The stuff about pulumiConfig seems like it should come after.