Adding a How to Contribute using codespaces page

[SeqLaz]

Add a new page guide for contributing with GitHub Codespaces by:

1. Creating a new branch on the QField-docs repository.
2. Launching a GitHub Codespace.
3. Editing Markdown files and using the live preview.
4. Running the local MkDocs server for a full preview.
5. Staging, committing, and pushing changes using Git commands and the UI.
6. Running pre-commit checks to ensure quality.
7. Opening a Pull Request.

[duke-nyuki]

Task linked: QF-6491 Check if we can use GitHub Codespaces for qfield-docs

[beanzmo]

I like this but I think the page is not in the right place. I think we should add this under Technical Reference!

[suricactus]

@beanzmo please do not review yet, it needs technical/workflow confirmation first. I am the blocker here, but also this PR is a prematurely opened.