Support "allowedFilter" without a baseline file

One of the possible use cases of the `dependencyGuard` plugin is to restrict particular dependencies between modules of a multi-module project. For example, to restrict a feature-module as a dependency of a core-module in an Android project.

Such use case can easily be done via `allowedFilter` parameter of the `dependencyGuard` configuration. `dependencyGuard` plugin can be applied in the core-module with `allowedFilter = { !it.startsWith("feature-") }`. But a baseline file will also be created in such case, though it is not needed. For core-module we don't need to guard against dependencies changes, but only against particular dependencies themselves.

From this follows that there may be some configuration of the `dependencyGuard` plugin, that allows to specify `allowedFilter` without a baseline file creation.

One possible solution may be adding special function `noBaseline()`, that can be assigned to `baselineMap` to explicitly specify, that a baseline file is not needed. (using `baselineMap = { null }` for that is less explicit)

```kotlin
dependencyGuard {
configuration("releaseRuntimeClasspath") {
modules = true
allowedFilter = { !it.startsWith("feature-") }
baselineMap = noBaseline()
}
}
```

Another possible solution may be adding parameter `guardDiff` or `baselineFile` (default to `true`), that will control whether a baseline file will be created or not. But this solution has drawbacks:
- such parameter can be messed with parameter `baselineMap`
- it's easy to break guarding against dependencies changes by assigning `baselineFile = false`

```kotlin
dependencyGuard {
configuration("releaseRuntimeClasspath") {
modules = true
allowedFilter = { !it.startsWith("feature-") }
guardDiff = false
}
}
```

IMHO, the first solution is preferred, because it is more explicit.