chore(process_tracker): use const instead of String for business_status

[pixincreate]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

When below command is executed in sandbox DB, we get a set of "distinct" business_statuses that is specified for process tracker:

SELECT DISTINCT(business_status) FROM process_tracker;

For debugging and fun, execute to learn more about process tracker and its behavior:

SELECT DISTINCT(name, retry_count, business_status, status), created_at FROM process_tracker order by created_at desc LIMIT 10000;

The main goal for us here is to keep all the business_statuses in a single place, confined for ease of access and increased readability. This also helps us keep track of the statuses we use.

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

We need to keep a track of the statuses that we use in process_tracker

How did you test it?

This should not require any testing as the change done is here just a mere replacement of hardcoded string with consts. If needed, the changes can be verified by following #3712's instructions. Reproduced below:

Perform PSync call from connector like Checkout. Payment Status should go to processing state. Wait for process_tracker to kick in and do a force_sync on its own. Wait for the status to get updated. I had webhooks set up (invalid configuration), even that is verified to be working.

Command used in DB:

SELECT * FROM process_tracker ORDER BY created_at desc LIMIT 2;

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible

[SanchithHegde]

Other than that, looks good to me!