Where estimators can be configured for metric, the point of providing a parameter p is that it should be possible to switch between Manhattan and Euclidian and other Minkowski distances just by modifying p (without changing metric). However this is not possible where metric='euclidean' by default. Rather, where p is available, metric should be 'minkowski' by default.

We should change the default metric in OPTICS without deprecation as it has not been released. Elsewhere, we need to:

• Warn for two versions if the user has not set metric but has set p != 2
• Change the default metric to minkowski when that deprecation period is over.