add force_tz() and force_tzs() to timezoneLintRules

[jonathancallahan]

The goal of "timezone linting" is to enforce explicit use of a named timezone argument in any function that allows it.

The timezoneLintRules in this package consists of a set of "function" = "timezoneParameterName" entries including many (but not yet all) functions from the lubridate package. The task here is to include any lubridate functions that we have missed.

The timezoneLintRules list is currently defined in MazamaCoreUtils.R. This is where new entries should be added.

• add force_tz() and force_tzs()
• scour the lubridate package for others functions that accept timezones