CLI feature request: template substitution in pipelines

[keara-soloway]

We want to support "templating" values in the pipeline .yaml file from the CLI.

The idea is to have a pipeline.yaml something like this:

config: {}
pipeline:
- common.reader.YAMLReader:
    filename: ${input_file}
...

and use it with the CHAP CLI something like this (BUT NOT THIS, the way key:value pairs are supplied in the scheme below could be ambiguous wrt data type or if there is more than one templated variable):

CHAP --batch --template input_file:[file_0.yaml, file_1.yaml] pipeline.yaml 

which would be identical to using this pipeline.yaml:

config: {}
pipeline_0:
- common.reader.YAMLReader:
    filename: file_0.yaml
...
pipeline_1:
- common.reader.YAMLReader:
    filename: file_1.yaml
...

with this CHAP CLI command:

CHAP --batch pipeline.yaml