Content directory smart contracts: Channels tests part 1 (w/o curator groups)

We need some preserved initial state for bridge contracts to perform those tests (see: https://github.com/Joystream/joystream/issues/1681)

Tests to include:

Success cases (valid owner access)

Creating a channel - success case (owner)

• create a channel
• check if event was emitted
• check if channel exists in the storage contract

Updating channel metadata - success case (owner)

• create a channel
• update channel metadata
• check if event was emitted

Updating channel owner - success case (owner)

• create a channel
• update channel owner
• check if event was emitted
• check if the owner changed in the storage

Removing a channel - success case (owner)

• create a channel
• remove a channel
• check if event was emitted
• check is channel no longer exists in the storage contract (isExisting == false)

Failure cases (invalid member access)

Creating a channel - fail case (wrong member)

• try creating a channel as member without member access
• verify it fails (optionally: expect specific reason)

Updating channel metadata - fail case (wrong member)

• create a channel
• try to update metadata using different key (without access)
• verify it fails (optionally: expect specific reason)

Updating channel owner - fail case (wrong member)

• create a channel
• try to update owner using different key (without access)
• verify it fails (optionally: expect specific reason)

Removing a channel - fail case (wrong member)

• create a channel
• try to remove a channel using different key (without access)
• verify it fails (optionally: expect specific reason)

Success cases (valid curator access)

Updating channel metadata - success case (curator)

• create a channel
• use curator key to update channel metadata
• assert success

Disabling/enabling a channel - success case (curator)

• create a channel
• use curator key to disable channel
• check if event emitted
• check if channel is disabled (storage)
• use curator key to enable channel
• check if event emitted
• check if channel is enabled (storage)

Removing a channel - success case (curator)

• create a channel
• use curator key to remove a channel
• assert success

Start with the preserved initial state requirement in issue 1681 and inspect the bridge contracts and channel storage contract involved here. Implement the listed owner and curator success and failure cases, including event and storage assertions. Done means all specified channel operations are covered for valid and invalid access.