Expose Validation and Defaulting function for configurations

[sm43]

we expose multiple configuration through configmap, we want to expose this through operator using CR spec. for other components we maintain a list of configurations in operator https://github.com/tektoncd/operator/blob/b9c5b31cefc732bb4e97a2fb25a9c744a1b4780e/pkg/apis/operator/v1alpha1/tektonpipeline_types.go#L87 with its defaults values and validation rules. but for any new addition in any component we need to keep updating those, and sometime we miss adding new configurations.

we want PAC to expose 2 functions, Defaulting and Validation which takes input a map[string]string and set default values in Defaulting and validate values in Validation which we use directly in Operator webhook. If any new configuration is added in PAC it will get added in operator by updating dependency.