Add a list of forced casks

[paour]

Similar to the pinning system, it would be nice to mark a cask as forced so that just running brew cu would offer updating that cask.

Some apps have a bad auto-update implementation (dbeaver-community for example), so I'd rather update them with Brew, but having to write a long command defeats the purpose.

[ondrejfuhrer]

I would argue here that brew cu -a is not a "long" command to run, wouldn't you agree? That way we're way more explicit then multiple way of configuration making things a bit harder to "test" and verify that they work with any incoming changes.

for context: that's also one of the reasons why I didn't push more on finishing #174

having to write a long command defeats the purpose.

You can also create a alias for yourself to make it even smaller if needed.

alias bcu='brew cu -a'