Update workspaces docs

What does this MR do and why?

Update workspaces docs.

• Remove Workspaces references from doc/user/project/remote_development/index.md. Not sure what purpose does it serve especially because it cannot be connected from a backend spun up by Workpsaces(as it is protected by OAuth).
• Update doc/user/workspace/configuration.md to distinguish between setting up infrastructure and creating a workspace. We've have multiples folks getting confused and saying that they assumed the entire infrastructure had to be setup for each repository they wanted to create a workspace from.
• Update doc/user/workspace/index.md with some clarifications.

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