[R] [Docs] Document the lubridate functions we support in {arrow}

[asfimport]

Add documentation around the lubridate functionality supported in arrow. Could be made up of:

• a blogpost
• a more in-depth piece of documentation

Reporter: Dragoș Moldovan-Grünfeld / @dragosmg

Subtasks:

• [R] [Doc] Write a longer form documentation for the lubridate functionality

Related issues:

• [R] How to round the timestamps in a mutate statement? (is related to)

_{Note: This issue was originally created as ARROW-16319. Please see the migration documentation for further details.}

[asfimport]

Todd Farmer / @toddfarmer:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned per project policy. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.

[asfimport]

Nicola Crane / @thisisnic:
Do we think this is now redundant due to the completion of ARROW-15011?

[asfimport]

Nicola Crane / @thisisnic:
Closing this for now as the new package documentation in ARROW-15011 shows us what we have implemented, and we can reopen this or open a new ticket if we decide we need something more detailed.