rarefaction - add multiple iterations option

[leppott]

Is your feature request related to a problem? Please describe.
Add option in rarefaction (or a new function) to calculate multiple iterations of rarefaction.

Describe the solution you'd like
See MBSS code (2025).
Calculate 1000 iterations and then calculate mean (and round to 0 decimals).

Describe alternatives you've considered
Can do on own but have done twice so would be good as a built-in function.

Additional context
Include options of doing in parallel with foreach and doParallel packages. (Also, MBSS code 2025)