Allow us to define context values using YAML instead of JSON.

Allow us to define context values using YAML instead of JSON.

### Use Case

Defining context using YAML will allow us to add comments. Looks like we have taken a step backwards. CFN used to require us to use JSON and then finally allowed us to use YAML. Now we have this great new tool but are required to use JSON again.

### Proposed Solution

Allow us to define context values using YAML instead of JSON, such as a cdk.context.yaml

### Other

* [ ] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

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This is a :rocket: Feature Request

No files or tests are named. Start by locating the AWS CDK context-value loading entry point and determine how cdk.context.json is parsed; done means context values can also be defined in cdk.context.yaml, including comments, without losing existing JSON support.

Written by the indexing model from the issue text.