## Changes
Originally, these blocks were merged with overrides. This was
(inadvertently) disabled in #94. This change re-enables merging these
blocks with overrides, such that any field set in an environment
override always takes precedence over the field set in the base
definition.
## Tests
New unit test passes.
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)
```
Pieter Noordhuis