Add API call functionality to create posting

[briantu]

Ticket link

Closes #88

Implementation description

• Added the create posting mutation in CreatePostingReviewPage
• Added two buttons ("Save as Draft" and "Post") in CreatePostingReviewPage that call the create posting mutation
  • Save as Draft: creates posting with status DRAFT
  • Post: creates posting with status PUBLISHED
• CreatePostingReviewPage gets posting data using PostingContext

Steps to test

1. Run the application locally docker-compose up --build
2. Create a branch in your local database for the posting to use
3. Click on the "Edit Posting" tab on the default page and enter the branch id of the branch you just created.
4. Add other dummy information (be sure to include the dates for "Start Date", "End Date", and "Auto-Closing Date").
5. Click on the "Review Posting" tab and click the "Save as Draft" or "Post" button
6. Check that the posting was successfully created in your local database

What should reviewers focus on?

• Create posting functionality works as expected
• Correct coding practices for calling API

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

[briantu]

Question to consider - how are we handling front-end error messaging? (e.g. when API call to create posting fails)

[github-actions]

Visit the preview URL for this PR (updated for commit ec9011b):

https://sistering-dev--pr147-brian-posting-review-3rdzcdsz.web.app

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[LenaNguyen]

sorry for the late review .-.

[LenaNguyen]

Nice discovery of useBoolean!