docs: added ideogram AIG provider

[roerohan]

Summary

Added docs for ideogram provider in AI Gateway.

Screenshots (optional)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/ai-gateway/	@abhishekkankani, @palashgo, @thebongy, @roerohan, @kathayl, @mchenco, @cloudflare/pcx-technical-writing

[github-actions]

Preview URL: https://d9fa2030.preview.developers.cloudflare.com
Preview Branch URL: https://rmukherjee-ideogram.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/ai-gateway/usage/providers/ideogram/	https://rmukherjee-ideogram.preview.developers.cloudflare.com/ai-gateway/usage/providers/ideogram/