#159623447 Create API documentation

[olusoladavid]

What does this PR do?

Creates complete API documentation for existing API endpoints based on Swagger

Description of Task to be completed

• Create documentation
• Ensure consistency of validation messages in documentation and API

How should this be manually tested?

• Pull branch into local repo and run npm run dev
• Point browser to http://localhost:3000/api/docs
• Documentation will be deployed to https://my-diary-api.herokuapp.com/api/docs

What are the relevant pivotal tracker stories?

#159623447

[coveralls]

Pull Request Test Coverage Report for Build 111

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 80.87%

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Totals
Change from base Build 109:	0.2%
Covered Lines:	144
Relevant Lines:	170

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💛 - Coveralls