Allow 127.0.0.1 to make self hosting easier + add an env...

We've had 3+ support issues in the past few weeks where users have configured redirects pointing to 127.0.0.1. Another user configured a heathcheck to request at 127.0.0.1. These should have just worked and we should just allow these hosts to access the backend preventing this class of error entirely.

I also added a new environment variable which will let users add extra hosts which can be very useful in some situations. E.g. if you have a reverse proxy which redirects to another host on a private network rewriting the host header, previously there is no easy way to configure Baserow to allow this. Now they can set BASEROW_EXTRA_ALLOWED_HOSTS="internal_baserow_hostname_or_ip".

Testing notes

1. Now can access Baserow's backend from 127.0.0.1
2. Can set BASEROW_EXTRA_ALLOWED_HOSTS and access the backend via the added hosts, both in the docker-compose setup and all-in-one

Merge Request Checklist

• changelog.md has been updated if required
• New/updated Premium features are separated correctly in the premium folder
• The latest Chrome and Firefox have been used to test any new frontend features
• Documentation has been updated
• Quality Standards are met
• Performance: tables are still fast with 100k+ rows, 100+ field tables
• The redoc API pages have been updated for any REST API changes
• Our custom API docs are updated for changes to endpoints accessed via api tokens
• The UI/UX has been updated following UI Style Guide