Support mixins without `vendor pull`

### Describe the Feature

I have components that are developed in the same repo as my stacks, I still want to use mixins with them. We would not need to use `source` or `atmos vendor pull`

A possible solution is an `atmos vendor mixin -c component`

### Expected Behavior

to be able to update mixins without `vendor pull`

### Use Case

To use mixins without vendor pull-ing any remote files

### Describe Ideal Solution

A possible solution is an `atmos vendor mixin -c component`

### Alternatives Considered

_No response_

### Additional Context

_No response_