## Changes
In 0.217.0 we started to emit warning on unknown fields in YAML
configuration but wrongly considered YAML anchor blocks as unknown
field.
This PR fixes this by skipping normalising of YAML blocks.
## Tests
Added regression tests
While working on artifact upload and workspace interrogation I realized
this mutator interface needs to:
1. Operate at the whole bundle level so it can apply to both
configuration and internal state
2. Include a `context.Context` parameter for a) long running operations
and b) progress reporting
Previous interface:
```
Apply(*config.Root) ([]Mutator, error)
```
New interface:
```
Apply(context.Context, *Bundle) ([]Mutator, error)
```