Added Shared Interfaces and Data Parsing for Github Activity

[henit-chobisa]

Additions

Added Separate Interface IGithubActivity as a type for fetched Github Activity Data, along with some auxiliary interfaces such as IGithubComment & IGithubPullRequest, also added a parser for parsing raw data into IGithubActivity Interface and return it.

Acceptance Criteria fulfillment

• [x] Implement IGithubAcitivity Interface, wtih IGithubComment & IGithubPullRequest
• [x] Make a parser that takes raw JSON data and parse it to IGithubActivity Interface.
• [x] Modify fetching Github Activity and return List of IGithubActivity

Adds up to #57