Ability to use code snippet from GitLab

[ydcjeff]

Clear and concise description of the problem

Followup of #4

Having to include base64 urls in the docs makes the docs unable to scan.

Suggested solution

• Fetch the code snippets/examples from GitLab and display them in the code editor pane.
• URL can be like <netlify-subdomain>/?gitlab/<username or org>/repo/tree/dir/main.py.
• Use fetch to get content from GitLab raw url.
• Replace the original url with the url stated above.

Alternative

N/A

Additional context

N/A

[ydcjeff]

Tried to fetch the raw content from GitLab and GitLab server for raw is missing access-control-allow-origin header. If someone knows the alternative way, please comment below.