model: Catboost: Add model catboostregressor and catboostclassifier

[nitesh585]

Catboost - https://github.com/catboost/catboost
To add model in dffml - https://intel.github.io/dffml/master/tutorials/models/index.html

[rajpratyush]

Can I work on this issue?

[johnandersen777]

@rajpratyush Yes! (See https://intel.github.io/dffml/master/contributing/dev_community.html#communication-style)

[aryanxk02]

@nitesh585 hello, where in the tutorial page is it mentioned on adding a new model in dffml module?

[aryanxk02]

okay got it @nitesh585

[Saanidhyavats]

I want to contribute on this issue and will be creating a pr within 2 days.