Develop Applications overview page redesign

[likidu]

We want to redesign this developer overview page to be more as a hub page that contain an better overview of:

https://docs.pingcap.com/tidbcloud/dev-guide-overview

• Available MySQL tools that compatible with TiDB Cloud
• Available ORM libs
• Links to TiDB basics
• Link to examples

• Cross link https://docs.pingcap.com/tidbcloud/secure-connections-to-serverless-clusters to this page as this link is embedded in the Connect popup which gains lots of traffic.

[likidu]

Engineering will start around end of November.

[Yuiham]

The development work is done.
I ran into issues while building codes in the preview environment. It will spend 2 days making some adjustments to the preview branch of the staging repo.