Slack: Feature - Adding get channel and archive channel actions

[jumpleby-splunk]

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Pull Request Checklist

Please check if your PR fulfills the following requirements:

• Testing of all the changes has been performed (for bug fixes / features)
• The manual_readme_content.md has been reviewed and added / updated if needed (for bug fixes / features)
• Use the following format for the PR description: <App Name>: <PR Type> - <PR Description>
• Provide release notes as part of the PR submission which describe high level points about the changes for the upcoming GA release.
• Verify all checks are passing.
• Do NOT use the next branch of the forked repo. Create separate feature branch for raising the PR.
• Do NOT submit updates to dependencies unless it fixes an issue.

Pull Request Type

Please check the type of change your PR introduces:

• New App
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Documentation
• Other (please describe):

Security Considerations (REQUIRED)

• If you are exposing any endpoints using a REST handler,
  please document them in the manual_readme_content.md.
• If this is a new connector or you are adding new actions
  • Please document in the manual_readme_content.md all methods (eg, OAuth) used to authenticate
    with the service that the connector is integrating with.
  • If any actions are unable to run on SOAR Cloud, please document this in the manual_readme_content.md.
• Are you introducing any new cryptography modules? If yes, please elaborate their purpose:
• Are you are accessing the file system? If yes, please verify that you are only accessing paths returned through
  the Vault API.
• Are you are marking code to be ignored by Semgrep with nosemgrep?
  If yes, please provide justification in an additional comment next to the ignored code.

Release Notes (REQUIRED)

• Provide release notes as part of the PR submission which describe high level points about the changes for the upcoming GA release.
• Adding a get channel function to be able to search for a splunk channel ID by name, or also return full channel information via channel ID
• Adding an archive channel function to be able to archive channels automatically via playbook capability

What is the current behavior? (OPTIONAL)

• Describe the current behavior that you are modifying.

What is the new behavior? (OPTIONAL)

• Describe the behavior or changes that are being added by this PR.
  described in release notes - archive and get channel functions

Other information (OPTIONAL)

• Any other information that is important to this PR such as screenshots of how the component looks before and after the change.

Pay close attention to (OPTIONAL)

• Any specific code change or test case points which must be addressed/reviewed at the time of GA release.

Screenshots (if relevant)

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Thanks for contributing!

[splunk-soar-connectors-bot]

Thank you for your submission! We have a total of 13 PRs open right now, and we are working hard on all of them! We will take a look as soon as we can.

[splunk-soar-connectors-bot]

@jumpleby-splunk Static Tests results for commit 88ffbfd - https://drive.google.com/file/d/16SORO_GQgIaTf5Oih02ykKpaJ6prUbvm/view?usp=drivesdk

[splunk-soar-connectors-bot]

@jumpleby-splunk Compile Tests results for commit 88ffbfd - https://drive.google.com/file/d/1CuQF5EjPIyB8VH3FA5w-rUtNgB2dYLTR/view?usp=drivesdk