Slack-watchman

Fixed
- Fixed a bug where an exception was raised when no suppressed signatures were passed. Fixes [66](https://github.com/PaperMtn/slack-watchman/issues/66)
- Fixed error when creating a Workspace object using the response from the Slack API. Validation was expecting a `bool`, but in some instances, a string was being returned. Fixes [68](https://github.com/PaperMtn/slack-watchman/issues/68)
- Fixed bug where the incorrect error message was being passed when environment variables were not set. Fixes [67](https://github.com/PaperMtn/slack-watchman/issues/67)

Added
- Ability to disable signatures by their ID in the `watchman.conf` config file.
- These signatures will not be used when running Slack Watchman
- Signature IDs for each signature can be found in the [Watchman Signatures repository](https://github.com/PaperMtn/watchman-signatures)
- App manifest JSON file for creating the Slack Watchman Slack application added in `docs/app_manifest.json`
- Pylint configuration and implement fixes and recommendations based on findings
- Added Pylint checks in GitHub actions
- Additional tests added:
- Unit tests for remaining non-model modules
- Integration tests for slack_client.py

Fixed
- Bug where variables were not being imported from watchman.conf config file

Changed
- Timestamps are now in UTC across all logging for consistency
- Refactor some commonly used functions into a utils module
- More general code cleanup and refactoring

Fixed
- Fixed a few bugs with models for User, Workspace and Messages not picking up all values

Added
- GitHub actions for Python tests and Docker build and run testing
- Implemented unit tests for models

Added
- Added enumeration of conversations with populated Canvases attached. These can contain sensitive information, and are worth reviewing.
- Added join domain to unauthenticated probe. This is the link to use to sign into a Workspace if you have an email with one of the approved domains.

Added
- Added enumeration of authentication options for the Workspace you authed to.
- Shows which domains are authorised to create accounts on the workspace. If a historic domain that isn't registered anymore is still approved, you could access this workspace using an email from it.
- Also shows which OAuth providers are authorised for the workspace.
- Added new 'unauthenticated probe' mode. This mode will attempt an unauthenticated probe on the workspace and return any available authentication information, as well as any other useful information such as whether the workspace is on a paid plan.
- No authentication token is required in this mode, you can spray away to any workspace you like.

Changed
- Signatures are now downloaded, processes and stored in memory instead of writing to disk. This saves having to store them in files, and solves the issues when using Slack Watchman with read-only filesystems (raised in [51](https://github.com/PaperMtn/watchman-signatures/issues/51))
- Migrated to Poetry for dependency control and packaging

Added
- Added notification for an invalid cookie being passed (Fixes [47](https://github.com/PaperMtn/watchman-signatures/issues/47))
Fixed
- JSON output for User and Workspace information was malformed, this has now been fixed