docs: performance

[jacobsfletch]

Payload is designed with performance in mind, but its customizability means that there are many ways to configure your app that can impact performance.

While Payload provides several features and best practices to help you optimize your app's specific performance needs, these are not currently well surfaced and can be obscure.

Now:

• A high-level performance doc now exists at /docs/performance
• There's a new section on performance within the /docs/queries doc
• There's a new section on performance within the /docs/hooks doc
• There's a new section on performance within the /docs/custom-components doc

This PR also:

• Restructures and elaborates on the /docs/queries/pagination docs
• Adds a new /docs/database/indexing doc
• More

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