fix(config): remove trailing newlines in regexes (#373)

Closes #372

Fun YAML fact of the day:

What is the difference between how these two expressions are parsed?

```yaml
foo: >
  bar
```

```yaml
foo: >-
  bar
```

They are invisible in yaml, but when you evaluate them to JSON the
difference is obvious:

```json
{
  "foo": "bar\n"
}
```

```json
{
  "foo": "bar"
}
```

User-Agent strings, URL path values, and HTTP headers _do_ end in
newlines in HTTP/1.1 wire form, but that newline is usually stripped
before the server actually handles it. Also HTTP/2 is a thing and does
not terminate header values with newlines.

This change makes Anubis more aggressively detect mistaken uses of the
yaml `>` operator and nudges the user into using the yaml `>-` operator
which does not append the trailing newline.

I had honestly forgotten about this YAML behavior because it wasn't
relevant for so long. Oops! Glad I released a beta.

Whenever you get into this state, Anubis will throw a config parsing
error and then give you a message hinting at the folly of your ways.

```
config.Bot: regular expression ends with newline (try >- instead of > in yaml)
```

Big thanks to https://yaml-multiline.info, this helped me realize my
folly instantly.

@aiverson, this is official permission to say "told you so".

Signed-off-by: Xe Iaso <me@xeiaso.net>

docs/docs/CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- Ensure regexes can't end in newlines ([#372](https://github.com/TecharoHQ/anubis/issues/372))
 - Add documentation for default allow behavior (implicit rule)
 - Enable [importing configuration snippets](./admin/configuration/import.mdx) ([#321](https://github.com/TecharoHQ/anubis/pull/321))
 - Refactor check logic to be more generic and work on a Checker type