APIv2 Versioning: apiLevel should be parsed for major.minor and should be required

[sfoster1]

overview

When we parse the contents of the apiLevel metadata key, we check for the exact strings 1 and 2. Instead, we should check for either 1 (to provide backwards compatibility with previously written protocols or 2.x. Leading zeroes do not need to be supported.

The version stored in a Protocol object should be an enum that provides both major and minor versions. Downstream consumers should also be updated to handle this enum.

If a version is not specified, there should be an exception.

Test cases:

should parse with api level 1.0:

metadata = {'apiLevel': '1'}

from opentrons import robot, instruments

should parse with api level 2.0:

metadata = {'apiLevel': '2.0'}

def run(ctx): pass

should parse with api level 2.5:

metadata = {'apiLevel': '2.5'}

def run(ctx): pass

should raise an exception explaining the correct format of the version:

metadata = {'apiLevel': '2.5.1'}

def run(ctx): pass

metadata = {'apiLevel': '2'}

def run(ctx): pass

should raise an exception requiring the presence of an api version:

def run(ctx): pass