docs: Add mission to Introduction, refactor Contact Us, and add About Us

[adam-hurwitz]

• Add Safe’s mission to the Introduction
• Refactor Contact Us into Community and Support sections
• Add Safe support options
• Add About Us and investors
• Merge the Safe open info Community and support page 1 into the Safe docs and remove the existing Safe open info Community and support page once merged.
• Add assets under management (AUM) to the Security overview page.

[germartinez]

Thank you for this Pull Request :)

[adam-hurwitz]

Thank you for approving @germartinez! 🙏🏻

I'm looking forward to seeing the updates go live on docs.safe.global and removing the duplicate content from Safe open info.

Questions/notes on the small fixes

• Do you think including a call-to-action for contributions to the docs will add value?
• A link to the help center could be good for builders with more specific product questions.
• Safe Ecosystem Foundation (SEF) background: If the docs are not the best place for this having an About or Team section on safe.global would potentially add valuable context for those new to the ecosystem.