Longer billing periods

[sbrossie]

This is a consolidation from killbill/killbill-api#78

Add support for:

• triennial
• quadrennial
• quinquennial
• etc. (up to 10 years)
• every 31 days
• every 18-months

[pierre]

31 days has also been requested: https://groups.google.com/g/killbilling-users/c/Z9Xw8R10V_k/m/XW15hgP4AAAJ

[pierre]

For reference, additional requests (out of scope for this ticket):

• Every Mondays
• First Monday of every month
• Second Monday of every month
• First Sunday of every quarters
• Second Sunday of first biannual of year

[ghost]

What if we used this wording instead?

every 3 years
every 4 years
every 5 years
[...]
every 10 years
every 31 days
every 18 months

I realize it doesn't match the existing nomenclature, but it's better to be clear than be consistent (in this case).

[pierre]

See killbill/killbill-api#104 and killbill/killbill-admin-ui#310.