Add yaml include support

[yhwen]

Fixes # .

Description

Added the support for yaml to include another yaml configuration file.

YAML does not naturally support any kind of "import" or "include" statement to include another yaml file. Adding this to support the yaml config in the format like: (include could be single file, or a list of include files.)

....
include: 1.yml

or:
include: [1.yml, 2.yml]

The "include" can be used at any level. Also support recursively include.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Quick tests passed locally by running ./runtest.sh.
• In-line docstrings updated.
• Documentation updated.

[chesterxgchen]

Should add description and unit tests to show how this supposed to be used ?

[yanchengnv]

Please explain why this feature is needed.

[yhwen]

Please explain why this feature is needed.

Added the description of how to use the "include". Also include the example in the unit_test.

api_version: 3
name: example_project

include: 1.yml

participants:

• name: server
  port: 123
  include: [1.yml]
• name: client
  port: 234
  include: 2.yml