[FEATURE REQUEST] Inspect Task position in Queue by LPOS

[slhmy]

Is your feature request related to a problem? Please describe.
Some like: while running asynq task inspect, the position of the task in a queue can also be printed.

Describe the solution you'd like
According to the official document, LPOS is available since Redis 6.0.6 which can get the elements index from a list. In this case we may simply query in the pending list, then we can get the task's position.

Describe alternatives you've considered
Give an option in the config to control wether this feature should be enabled (disabled by default?), which can hold the cases when some user is using Redis in version lower than 6.0.6.