Consolidate VCS integration guides with org/user/project/pipeline content

[rosieyohannan]

Description

The main change in this PR is: Create new page: Users, organizations and integrations guide

• Bring in all content from VCS integration pages into this one page and describe feature support byt user/org type/integration type/pipeline type.

• Archive VCS-specific integration pages

This PR also includes many fixes for cross references which have had to be updated due to the move of all this content

Reasons

Why did you make these changes?

Content Checklist

Please follow our style when contributing to CircleCI docs. Our style guide is here: https://circleci.com/docs/style/style-guide-overview.

Please take a moment to check through the following items when submitting your PR (this is just a guide so will not be relevant for all PRs):

• Break up walls of text by adding paragraph breaks.
• Consider if the content could benefit from more structure, such as lists or tables, to make it easier to consume.
• Keep the title between 20 and 70 characters.
• Consider whether the content would benefit from more subsections (h2-h6 headings) to make it easier to consume.
• Check all headings h1-h6 are in sentence case (only first letter is capitalized).
• Include relevant backlinks to other CircleCI docs/pages.