Creates foundation documentation

[busrasengul]

Adds documentation for the Backoffice foundation,
providing resources on core concepts, communication, data management, and UI development.

📋 Description

Checking, adding, rewording foundation page

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• [ x ] Sentences are short and clear (preferably under 25 words).
• [ x ] Passive voice and first-person language (“we”, “I”) are avoided.
• [ x ] Relevant pages are linked.
• [ x ] All links work and point to the correct resources.
• [ x ] Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

V17

Solves #7568 too.

[jacksorjacksor]

LGTM!

[Luuk1983]

No comments on the foundation stuff, except one about the context-api articles I changed and you copied over from Umbraco 16;

It also needs an update to the menu structure in 17/umbraco-cms/SUMMARY.md because the foundations page is new. Please check the original pull request: https://github.com/umbraco/UmbracoDocs/pull/7565/files#diff-f260d7f0885a3216616d8e1aeee1a64b7df1db6fba00b1f01f4f52dcd688546b

[Luuk1983]

The change to the menu structure that was done for context-api (because the fundamentals page is new) need to be done as well for the Umbraco 17 docs.