add reporeader interface and an example extractor for python

[davidgamero]

Description

add a new interface and pattern for extracting defaults from a repo in draft.
the current pattern only supports using pre- set defaults, which can then be replaced by a user-provided value.

Similar to the way the TemplateWriter interface was used to abstract the filesystem writing operations, this PR introduces the RepoReader interface that abstracts reading data from a repo's files.

The main goal of this is to allow more intelligent defaults such as detecting a compatible image version or entrypoint script by reading the files in a repo during draft create execution.

By allowing prompt defaults to be set through extracting information from the repo files, we can greatly improve the probability that a default value is correct.
An example of this is the great work on #214 that could leverage this interface to standardize how we read data from the repo and organize the procedure using extractors that each apply to specific languages

Fixes # (issue)
Feature # (details)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Existing unit and integration tests pass

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[hsubramanianaks]

@davidgamero looks good except a question I had. Great improvement to draft, thanks David.