[RFC] Make dynaconf CLI configurable for file to look at and validator to apply

**Is your feature request related to a problem? Please describe.**
I have several configuration files in a project used for different purposes. I would like to have separate text-based validator schemas for these. Right now it seems as though there is exactly one configuration file that is support (`config.toml`) with exactly one validator schema (`dynaconf_validators.toml`). It seems ironic to me that `dynaconf` itself is not configurable as to which configuration file to validate and with which validation/schema file.

**Describe the solution you'd like**
```
dynaconf -c path/to/my_special_config.toml validate --schema etc/config_schemas/my_special_validator_schema.toml
```

**Describe alternatives you've considered**
* Patching the code
* Writing a wrapper script that will copy the validator and all config files into a temporary working directory with files renamed to the expected (apparently hard-coded) filenames, and executing `dynaconf validate` there.

**Additional context**
None. But overall: Dynaconf is great, and I'm happily using it *except* for this one point which is an annoyance.