Add get and list workflows from github actions API

[hvardhanx]

Hi @Abhi347!

Here is a small PR which adds get and list workflows from Github Actions API:

• List Workflows: https://docs.github.com/en/rest/actions/workflows#list-repository-workflows
• Get Workflow: https://docs.github.com/en/rest/actions/workflows#get-a-workflow

Added tests as well for code coverage

[hvardhanx]

@ebk45 a small ping for review 🙂

[ebk45]

Although this client looks great, it would be appreciated if you could follow the existing nesting pattern we have established that follows the GitHub API. In this case, you'd need to create a parent ActionsClient and then your WorkflowsClient can be instantiated from there.

There's many examples of this around the codebase, for instance here issues are nested under repos, so you create an issue client from a repo client: https://github.com/spotify/github-java-client/blob/master/src/main/java/com/spotify/github/v3/clients/RepositoryClient.java#L119

[hvardhanx]

Thank you so much for the review @ebk45! I have updated the pull request and added ActionsClient under RepositoryClient and WorkflowsClient is now a child of ActionsClient. Please let me know if I need to change anything. 🙂

[hvardhanx]

small ping for review @ebk45 🙂

Out of office for the coming 6 months

[hvardhanx]

Thanks a lot! @dennisgranath 😄

[hvardhanx]

Adds ActionsClient for #18