RFC: Allow dot traversing for validators

[rochacbruno]

Depends on #84

Traversal of nested dictionaries should also be possible in validators.

having settings.yaml

DEFAULT:
    REDIS:
        HOST: localhost
        PORT: 1234

It is currently possible to write validator to ensure:

REDIS key is set and it is a dict and it has the keys HOST and PORT being HOST a str and PORT as int

from dynaconf import settings, Validator

settings.validators.register(
    Validator(
        'REDIS', 
        must_exist=True, 
        is_type_of=dict.
        condition=lambda v: (
            'HOST' in v and 'PORT' in v
        ) and (
            isinstance(v.HOST, int) and isinstance(v.PORT, int)
        )
    ),
)

RFC: Allow the above validation to be written using dot notation

settings.validators.register(
    Validator('REDIS',  must_exist=True,  is_type_of=dict),
    Validator('REDIS.HOST', must_exist=True, is_type_of=str),
    Validator('REDIS.PORT', must_exist=True, is_type_of=int),
)

Also the above validation can be translated to toml validator file as in https://dynaconf.readthedocs.io/en/latest/guides/validation.html#cli-and-dynaconf-validators-toml

[suvratjain1995]

@rochacbruno I would like to work on this enhancement.

[rochacbruno]

@suvratjain1995 cool! this issue depends on the implementation of #84

[jperras]

Sorry for the issue noise – I didn't realize that my forced push rebasing onto my own fork feature branch would cause multiple activity references here. I'll avoid linking the issue no. in commit messages from now on.