Update LMSPublisher to not convert price to integer

[julianajlk]

REV-1632.

Background:
The min_price column in LMS CourseMode table takes integers, and should be updated to take decimals to match the price in ecommerce database, making the price across the learner pathway to purchase the same (49.99 vs. 49).

This ticket covers:
Currently, ecommerce serializes the price as an int before sending a request to LMS - this ticket removes this conversion so that it's converted to a float instead, keeping the digits, then LMS will handle the conversion to the appropriate type it needs in the CourseMode table.

In order to decrease the risk of breaking anything with migrations, this change will be divided into 5 steps across edx-platform and ecommerce:

1. Deploy LMS no.1 (PR here): make sure min_price can receive non-int.
2. Deploy ecommerce no.1 (this PR): change LMSPublisher to stop converting min_price to int.
3. Deploy LMS no.2 (WIP PR here): add new column for price and make sure it's populated with the same min_price, and that min_price can receive a Decimal.
4. Deploy LMS no.3 : use new price column in Track Selection and Course Home pages.
5. Deploy LMS no. 4 : remove original min_price column.

[julianajlk]

Closing as this work was reprioritized.