docs: fix some mistakes in Environment API guides

[silvenon]

Description

I love the Environment API. Here are a few important fixes to the guides to help people when trying it out:

• rename a reference from a non-existent node environment to server
• remove the usage of the non-existent vite-environment-provider package
• references to environments were generic-sounding in some guides (environment), and specific in others (ssrEnvironment), so I made them all specific, which I believe is good practice anyway
• there is advice that ssr environment can be called server as well, which is arguably misleading because creating a server environment would not receive any of the built-in ssr configuration, so I simply removed this sentence

[silvenon]

Wow, I sure did suck at this 😆 Thanks for being so constructive about it, though, and let me know if there's anything else.

[patak-cat]

Oh, no problem! It is good to see where you are finding difficulties in the docs. I'll let others check the PR to see if they would like to change the environment names as you proposed. To be honest, I'm fine with the names we had (except for the typo you corrected with environment.node)