feat(integration): add omnivore support

[colmugx]

Description

Added Omnivore integration.

Tips:

• Omnivore supports self-hosting, so an additional endpoint in settings.

（添加了我第一喜欢的 Read it later 服务）

Linked Issues

#677

Additional context

TODO:

• [ ] i18n (another pull request)

Screenshots

[vercel[bot]]

@colmugx is attempting to deploy a commit to the RSS3 Team on Vercel.

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