docs(queue): update bull connection option

[a7urag]

Fixed BullModule.forRootAsync redis parameter to connection as per implementation

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What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [x] Docs
• [ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

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• [x] No

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