New issue type: Performance improvements

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Just a heads up: We've introduced a new issue type to capture performance concerns.

These have been difficult to effectively convey using the other issues templates as they're typically not quite features and not quite bugs. The new issue type and template allow us to clearly categorize performance concerns.

NetBox powers some of the biggest and fastest-growing networks in the world. You'll see a renewed focus on identifying opportunities to improve performance across all dimensions over the next few months, to ensure it keeps up with the thousands of innovators who rely on it.