It should be possible to line break CEL validation expressions

We have CEL expressions that are more than 700 characters long and completely unreadable due to the fact that they have to be defined as one single long line. We should find a way to allow defining them over multiple lines.

The issue does not name a file, test, or entry point. Start by locating how controller-tools parses and emits CEL validation expressions, then determine where line breaks are rejected or lost; done means expressions can be defined across multiple lines without changing their validation behavior.

Written by the indexing model from the issue text.