🐛 Fixed Tips & Donations checkout error for sites with long titles

[kevinansfield]

ref https://linear.app/tryghost/issue/ONC-296

Our stripe_prices.nickname field had a length of 50 chars which meant we could error out trying to save a donation Stripe price with a generated product nickname containing a long site title.

• updated db schema and added a migration to change column length to 255
• added truncation to nickname generation to enforce a limit of 250 chars to match Stripe's limit

[github-actions]

It looks like this PR contains a migration 👀
Here's the checklist for reviewing migrations:

General requirements

• Satisfies idempotency requirement (both up() and down())
• Does not reference models
• Filename is in the correct format (and correctly ordered)
• Targets the next minor version
• All code paths have appropriate log messages
• Uses the correct utils
• Contains a minimal changeset
• Does not mix DDL/DML operations
• Tested in MySQL and SQLite

Schema changes

• Both schema change and related migration have been implemented
• For index changes: has been performance tested for large tables
• For new tables/columns: fields use the appropriate predefined field lengths
• For new tables/columns: field names follow the appropriate conventions
• Does not drop a non-alpha table outside of a major version

Data changes

• Mass updates/inserts are batched appropriately
• Does not loop over large tables/datasets
• Defends against missing or invalid data
• For settings updates: follows the appropriate guidelines