Add dump.rdb to gitignore

[pamelafox]

Description

After running Redis locally, I noticed dump.rdb show up in my repository, which is apparently the Redis dump file. This PR adds dump.rdb to gitignore. I thought about putting it behind a "use_celery = y" guard, but realized Redis is also the caching mechanism, so it seems relevant for all configurations.

Checklist:

• I've made sure that tests are updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

I don't believe the dump file belongs in version control.

[browniebroke]

Can you explain shortly dow did you have this file show up in your project? I don't remember seeing it... Perhaps it's because I don't usually run Redis on my host machine?

[pamelafox]

Yep, I started redis-server command from the root of my project directory (my_awesome_project), and that saves dumps of the DB every so often.

my_awesome_project % redis-server

I suspect this is what creates dump.rdb:

98819:M 06 Jan 2023 11:06:00.036 * Background saving started by pid 4499
4499:C 06 Jan 2023 11:06:00.046 * DB saved on disk

I started it locally so that I could check how caching and celery worked locally before testing them on production.