Disable and Set Price Input Fields to 0 for Donation Offers and Request

[shjryan]

Description

When a user selects to create either a "donation offer" or a "donation request," the price input fields should be automatically disabled and set to 0.

Expected Behavior

1. Users should be able to select a checkbox whether the post is a donation or not.

When a user chooses to create a "donation offer" or a "donation request":

1. The price input fields should be disabled.
2. The price should be automatically set to 0.

Acceptance Criteria

• A new checkbox whether a post is donation or not is displayed on create/edit post pages.
• Price is automatically set to 0 for donation type posts.
• Proper validation and handling of the price field are maintained on both frontend and backend.