Config option for adding extra Jira fields

[jharuda]

It would be useful to have some easy way how to populate extra Jira fields with NEWA YAML config.
Those fields should include basic fields [1] and extended fields for Jira customized projects.

For example jira-project-config.yaml:

...
extra_fields:
  - pool_team: <team_name>
...

Such a config will add pool_team option to Jira tickets generated with NEWA.

[1] https://community.atlassian.com/t5/Jira-questions/List-of-Jira-fields-and-description/qaq-p/1558852

[kkaarreell]

This is being worked on in #105

[kkaarreell]

Implemented in #105