Use available channels from context

[jwm0]

I want to merge this change because it reduces the number of api calls and instead uses available channels from global state. Additionally this fixes the issue where users without MANAGE_CHANNELS permission cannot fetch basic channels metadata. An example would be a user with MANAGE_PRODUCTS who cannot see to which channels a product is available in.

QA instructions
The following views have changed and should work the same as our current staging:

1. Collection Create
2. CollectionUpdate
3. Sales Create
4. Sales Update
5. Voucher Create
6. Voucher Update
7. Product Create
8. Product Update
9. Shipping Zone Details

PR intended to be tested with API branch: master

Screenshots

Pull Request Checklist

1. This code contains UI changes
2. All visible strings are translated with proper context including data-formatting
3. Attributes [data-test-id] are added for new elements
4. Changes are mentioned in the changelog
5. The changes are tested in different browsers and in light/dark mode

Test environment config

API_URI=https://qa.staging.saleor.cloud/graphql/

[dominik-zeglen]

Just a quick note, I think availableChannels field can be dropped from AppChannelContext since it's just memozing apollo output

[jwm0]

Just a quick note, I think availableChannels field can be dropped from AppChannelContext since it's just memozing apollo output

Having them defined in context does us no harm and I believe it makes sense to include them together with the rest