Dedicated page on handling and improving performance

[joshuablum]

Could include things like:

• When to switch from flat-file to the Eloquent driver
• Handling assets and presets
• Using cache tags
• Server environments and specs
• Redis
• Selecting only certain fields
• Limiting depths

[jasonvarga]

There are some performance areas already which we should cross reference from this new page.

e.g.

• https://statamic.dev/tips/optimizing-assets
• https://statamic.dev/tags/nav#performance