feat: add support for pinning channels

[akupila]

CLA

• [ ] I have signed the Stream CLA (required).
• [ ] Code changes are tested

Description of the changes, What, Why and How?

This adds support for pinning and unpinning channels. The channel pin is stored on the user-channel relationship (channel membership). The backend API endpoint for this is not yet live.

Changelog

• Add support for pinning channels using updateMemberPartial
• Add channel.pin and channel.unpin
• Fix partialUpdateMember returning a type without the channel_member key that's returned from the API

[github-actions[bot]]

Size Change: +1.52 kB (+0.34%)

Total Size: 453 kB

Filename	Size	Change
dist/browser.es.js	98.5 kB	+338 B (+0.34%)
dist/browser.full-bundle.min.js	56.3 kB	+160 B (+0.29%)
dist/browser.js	99.7 kB	+345 B (+0.35%)
dist/index.es.js	98.6 kB	+336 B (+0.34%)
dist/index.js	99.8 kB	+340 B (+0.34%)

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