Add status field to Posting and update Posting types and resolvers

[briantu]

Ticket link

Closes #93

Implementation description

• Added status column in the Posting table as enum of values:
  • DRAFT
  • PUBLISHED
  • ARCHIVED
• Generated new migration file for status field
• Updated PostingRequestDTO and PostingResponseDTO and corresponding GraphQL types with the status field
• Modified PostingService CRUD methods to read/write the status value

Steps to test

1. We need row(s) in the skills, branches, and employees tables for testing which can be created using the GraphQL mutations or with raw SQL:

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');

2. Run docker exec -it sistering_backend /bin/bash -c "npx prisma generate"
3. Go to http://localhost:5000/graphql and verify that we can read/write the status field using GraphQL queries and mutations

What should reviewers focus on?

• Verify that we can read/write status field 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]

Code looks good for this ticket! 🔥 However, there's a small unrelated change that would be nice to sneak in as well (see comments for details)