Create Posting CRUD Methods and GraphQL Resolvers

[albertlai431]

Ticket link

Closes #50

Implementation description

• Implement CRUD methods:
  • getPosting
  • getPostings
  • createPosting
  • updatePosting
  • deletePosting
• Create corresponding GraphQL resolvers and DTOs
• Modified Postings Model in schema as requested in ticket and generated associated prisma migration file

Steps to test

1. Start docker and run docker-compose up --build
2. We need row(s) in the skills, branches, and employees tables for testing and will need to create those with raw SQL for now. Run the following commands:

docker exec -it sistering_db /bin/bash
psql -U postgres -d sistering
INSERT INTO branches (name) VALUES ('Branch1');
INSERT INTO skills (name) VALUES ('Skill1');
INSERT INTO employees (userId, branch_id) VALUES ('1','1');

3. Run docker exec -it sistering_backend /bin/bash -c "npx prisma generate" and run the lastest migration files using npx prisma migrate deploy
4. Go to http://localhost:5000/graphql and verify that all GraphQL queries and mutations introduced in this ticket work as expected

What should reviewers focus on?

• Verify that GraphQL endpoints work as expected

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[sherryhli]

Looking good so far! Will do a second review once this set of comments is addressed

[sherryhli]

Almost there, just a couple of minor things left!

[sherryhli]

LGTM! 🚢
(please coordinate the order of merging with the rest of the team as described in Slack)

[sherryhli]

Extra nit: can we rename these files to keep consistency with the other interface files?

backend/services/interfaces/IPostingService.ts -> backend/services/interfaces/postingService.ts
backend/services/interfaces/ISkillService.ts -> backend/services/interfaces/skillService.ts
backend/services/interfaces/IEntityService.ts -> backend/services/interfaces/entityService.ts