feat: Enable OAuth 3LO support

[christianarty]

Summary

fixes #863

This PR allows for users to have another option (oauth) when generating their JIRA config.yml for the Cloud installation.

Details

This PR implements JIRA's 3LO OAuth solution for users to obtain a JIRA access token.
Each consumer of jira-cli will need to create a JIRA App with the specific scopes in order to connect it properly with their JIRA cloud instance.

The oauth secret will be stored in the .config/.jira directory, where the tokens will be automatically regenerated when it expires and the newly generated tokens will be cached to the oauth secret file.

How to create a JIRA App properly:

See this discussion post here: #879 (comment)

Known Limitations/Issues

Note

This limitation has also been noted in the README under the Known Issues section.

Ideally, for OAuth, we would have one single distributed app that can be installed in multiple different JIRA cloud instances. However, The 3LO doesn't support Proof Key for Code Exchange (PKCE). Without this support, we would have to share the single distrubuted app's client secret with all the consumers. See these links for more info:

• https://jira.atlassian.com/browse/ECO-283
• https://community.developer.atlassian.com/t/oauth-2-0-with-proof-key-for-code-exchange-pkce/80173/3

As noted in the forum above, a workaround would be that each consumer has to create their own JIRA app and use that app's client ID and secret in the jira-cli client app.

• This basically acts like a proxy to funnel requests into your JIRA cloud instance

Testing Done

• make deps install => WORKS
• ~/go/bin/jira issue create -tTask -s"TEST TICKET" -l"testing" --template ~/jira/task.tmpl -a$(~/go/bin/jira me) => WORKS (created a ticket, and proper link)
• make test => WORKS
• make lint => WORKS
• make ci => WORKS

[shadyabhi]

cc: @ankitpokhrel for visibility. It'll be great if this can be reviewed/merged soon, so folks that can only authenticate through OAuth 3LO can start using this tool again.