feat(models): add report filename option

[BioPhoton]

The changes should help to improve testing of report generation. ATM all tests write in the same folder and with the same file name. Adding a filename option to core would improve the testing situation and is helpful in for integrations.

This PR includes:

• extending persistConfigSchema with filename and a default value
• add tests
• adopt models fixtures to follow new standard see Adjust testing strategy for fixture values #173

Implementing the CLI option is resolved in a followup PR

closes#161

[matejchalk]

It works nicely with the config 👍

The PR description is a bit misleading, --filename (or --persist.filename) doesn't work as a CLI argument. You'd have to add persist.filename to core-config-options.ts to make it accessible from the CLI (we should auto-sync those in the future, probably).

Also, I noticed the PR title doesn't follow our commit conventions - model scope should be models.