How Should the Schemas Work

## I'm submitting a...

- [ ] Bug report
- [ ] Feature request
- [x] Question

Please how should one deal with the schemas?

## Current behavior

Currently I define schema similar to how it is described in [docs](https://db-migrate.readthedocs.io/en/latest/Getting%20Started/configuration/#configuration)

Both migration table and migration content are created in the `public` schema.

Behavior is the same regardless of the defined schema existence.

## Expected behavior
* Defined schema is created if one doesn't exist.
* Migration table and content affect defined schema

## Minimal reproduction of the problem with instructions
```json
{
"defaultEnv": "def",
"def": {
"driver": "pg",
"host": {"ENV": "PGHOST"},
"port": {"ENV": "PGPORT"},
"database": {"ENV": "PGDATABASE"},
"schema": {"ENV": "PGSCHEMA"},
"user": {"ENV": "PGUSER"},
"table": {"ENV": "PG_MIGRATION_TABLE"},
"password": {"ENV": "PGPASSWORD"}
}
}
```
I've tried both `ENV` link and exact value

## What is the motivation / use case for changing the behavior?
Using data separation on schemas level

## Environment

db-migrate version: 1.0.0-beta.15, 0.11.12

plugins with versions: not sure I have one

db-migrate driver with versions: pg 1.2.2


Additional information:

- Node version: 14.17.0

- Platform:  Mac

Others: