Create CRUD functionality for "Post" domain and endpoints

[JHalvor]

Parent EPIC: https://github.com/boolean-uk/team-dev-client-ex-2410-team2/issues/6

[JHalvor]

approve please @uerbzr

[eyvmal]

Add the missing CRUD operations for the Post-object.

• Create
• GetAll
• GetById
• Delete

(UpdateById is created in another issue)

[eyvmal]

Added new endpoints for post:

• getById
• updateById
• deleteById

Updated endpoints for:

• create
• getAll

New files:

• domain/post.js

Updated files:

• routes/post.js
• controllers/post.js
• docs/openapi.yml

• prisma/schema.prisma

  All endpoints require the user to be logged in.

getById fetches a post with an id input parameter. updateById updates a post with an id input parameter and content body. deleteById deletes a post with and id input parameter. create creates a new post for the logged in user with a content body. getAll fetches all posts.

the domain/post.js file contains all database calls, and follows the format of the already existing domain/user.js. the controllers/post.js file is updated with all endpoint logic and error handling. the docs/openapi.yml is updated with the new endpoints and a new UpdatePost-schema. the prisma/schema.prisma is updated with two new fields for the post model (createdAt, updatedAt)