Allows to generate phpstan config with ignores list based on phpstan report (some kind of baseline)

Steps to create baseline ignores list:

1. Run phpstan to create errors list file: vendor/bin/phpstan analyse --memory-limit=-1 -l3 --error-format=json > phpstan-l3.json. You should note --error-format=json > phpstan-errors-list.json here, that's used to produce JSON of errors and put them to file phpstan-errors-list.json.
2. Run script to generate phpstan ignores config: php phpstan-ignore.php phpstan-errors-list.json > phpstan-ignore-config.neon. You should note phpstan-errors-list.json — that's JSON you used on the previous step; and also phpstan-ignore-config.neon — that's where generated phpstan config will be written to.
3. Include newly generated config to your main config file — add phpstan-ignore-config.neon to includes section of your main config. If you don't have a config file, or there is no includes section currently, here is the example: phpstan.neon:

includes:
    - phpstan-ignore-config.neon

That's it!