doc: add an umbrella page for CS Filecoin services

[LesnyRumcajs]

Summary of changes

Changes introduced in this pull request:

• added an umbrella page for Chainsafe's Filecoin services (potentially to be a redirect for filecoin.chainsafe.io

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[ansermino]

Just my two cents 🦐

[LesnyRumcajs]

@ansermino Changed it a bit to address some of your comments (mainly regarding the page being Forest-centric).

[ansermino]

Otherwise LGTM. Would be nice to expand over time but this is a great start