[PLGN-621] Add OAuth to ServiceNow Plugin (#2157)

[igorski-r7]

Proposed Changes

Description

Describe the proposed changes:

• Added OAuth authentication to the plugin

PR Requirements

Developers, verify you have completed the following items by checking them off:

Testing

Unit Tests

Review our documentation on generating and writing plugin unit tests

• Unit tests written for any new or updated code

In-Product Tests

If you are an InsightConnect customer or have access to an InsightConnect instance, the following in-product tests should be done:

• Screenshot of job output with the plugin changes
• Screenshot of the changed connection, actions, or triggers input within the InsightConnect workflow builder

Style

Review the style guide

• For dependencies, pin OS package and Python package versions
• For security, set least privileged account with USER nobody in the Dockerfile when possible
• For size, use the slim SDK images when possible: rapid7/insightconnect-python-3-38-slim-plugin:{sdk-version-num} and rapid7/insightconnect-python-3-38-plugin:{sdk-version-num}
• For error handling, use of PluginException and ConnectionTestException
• For logging, use self.logger
• For docs, use changelog style
• For docs, validate markdown with insight-plugin validate which calls icon_validate to lint help.md

Functional Checklist

• Work fully completed
• Functional
  • Any new actions/triggers include JSON test files in the tests/ directory created with insight-plugin samples
  • Tests should all pass unless it's a negative test. Negative tests have a naming convention of tests/$action_bad.json
  • Unsuccessful tests should fail by raising an exception causing the plugin to die and an object should be returned on successful test
  • Add functioning test results to PR, sanitize any output if necessary
    • Single action/trigger insight-plugin run -T tests/example.json --debug --jq
    • All actions/triggers shortcut insight-plugin run -T all --debug --jq (use PR format at end)
  • Add functioning run results to PR, sanitize any output if necessary
    • Single action/trigger insight-plugin run -R tests/example.json --debug --jq
    • All actions/triggers shortcut insight-plugin run --debug --jq (use PR format at end)

Assessment

You must validate your work to reviewers:

1. Run insight-plugin validate and make sure everything passes
2. Run the assessment tool: insight-plugin run -A. For single action validation: insight-plugin run tests/{file}.json -A
3. Copy (insight-plugin ... | pbcopy) and paste the output in a new post on this PR
4. Add required screenshots from the In-Product Tests section