Add channel points custom rewards creation feature

[Scorfly]

Update from twitch changelog 2021‑05‑24

• Polls and Channel Points Predictions Twitch API endpoints have moved from public beta to general availability.
• Polls and Channel Points Predictions EventSub subscription types have moved from public beta to version 1.

Update from twitch changelog 2021‑05‑21

• Extension Bits Transaction Create EventSub subscription type has been added as a public beta.
• Channel Points Custom Rewards - The API reference for Custom Rewards endpoints has been updated for consistency and to clarify conditional requirements for body parameters. For example, max_per_stream is required if a value for is_max_per_stream_enabled is also provided.

Update from twitch changelog 2021‑05‑14

• Channel Prediction Lock EventSub subscription type - corrected the name of the lock timestamp to locked_at.
• Channel Prediction End EventSub subscription type - removed the locked_at field due to edge cases with Predictions that are cancelled or closed early.
• Create EventSub Subscription and Get EventSub Subscriptions - limit removed following the new EventSub subscription limit cost-based system.
• Get Channel Information - Added delay to return values table and example payload.

[coveralls]

Pull Request Test Coverage Report for Build 880004386

• 13 of 13 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 96.127%

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Totals
Change from base Build 847537501:	0.04%
Covered Lines:	968
Relevant Lines:	1007

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💛 - Coveralls