add page size checks for sync/async request mode

[JessicaS11]

There's still a reference to using a smaller page size in examples/examples/ICESat-2_DAAC_DataAccess_Example.ipynb because it refers to synchronous requests. Note that this notebook indicates that synchronous requests are done by default, but I think this must be outdated. It looks like the request mode is async by default (https://github.com/icesat2py/icepyx/blob/development/icepyx/core/APIformatting.py#L446).

Given that the page size limit is only 100 when the request mode is synchronous, maybe we need another check somewhere that decreases the page size when a user overrides that default and uses synchronous mode?

Originally posted by @trey-stafford in #239 (comment)

[JessicaS11]

but I think this must be outdated

Or is an uncaught typo... I don't think sync was ever the default! Thanks for catching this.

[JessicaS11]

maybe we need another check somewhere that decreases the page size when a user overrides that default and uses synchronous mode?

Based on #87, this may also need to mandate that page_num is provided if sync request mode is used.