Updated standalone documentation and add new examples

[rehanvdm]

What issue does this pull request resolve?
Updates documentation for the standalone functionality, and adds examples of generating and consuming the generated validation code in both CJS and ESM formats. It also shows examples for single and multiple schemas.

Adds docs for the new ESM feature mentioned in #1523 and gives a concrete example of usage for #1831.

I tested the examples in the documentation below and have them in a separate private repo that I want to make public as soon as this new ESM feature gets released. I don't know if you maybe want to reference it? Or maybe fork it so that it lives under the ajv-validator organization and then reference to that from these docs.

What changes did you make?
Updated docs.

Is there anything that requires more attention while reviewing?
Don't think so, just possible revisions if required, let me know or go ahead and make them directly.