Influx CLI - allow bucket creation RP in 'd' units (days)

[abalone23]

Proposal:
Allow for buckets to be created with a retention policy in days "d" units. Note that in 1.x, duration units include days d and weeks w as well:
https://docs.influxdata.com/influxdb/v1.8/query_language/spec/#durations

Current behavior:

./influx bucket create -n testbucket -r 10d
Error: invalid argument "10d" for "-r, --retention" flag: time: unknown unit d in duration 10d

Desired behavior:
I would like for the "d" unit to be recognized when creating a bucket since it's typical to create RP in days, like 7d, 30d etc.

Alternatives considered:
Convert days to hours and use 'h' unit instead.

Use case:
Since most people create RPs in terms of days, this would eliminate having to convert to hours and be less confusing.

[jsteenb2]

I went ahead and added weeks as well to the CLI durations supported. Weeks will land in this PR: #18659