Skill Oracle+Database driver

[robinsonkwame]

The skill oracle is currently implemented with GET and PUT API calls but has no mechanism for automatically ingesting more skill candidates when needed. I've purposely left logic for this out of the service (although you can peek at _push_once unittest to see how it might be partially implemented).

For the end to end skills-labeller we need some kind of component that:

• Detects number of unlabeled candidates
• When number of unlabeled candidates is low, pushes unlabeled candidates from the database/db into the skill-oracle (as unlabeled candidates, via PUT)

(discussion in #mlops will be held, see what's a simple way to do this)