feat: select version parameter

[KyleTryon]

This is a re-implement of #25.
Thank you to the original author. We wanted to refactor the orb and quickly release a major change with some upgrades without needing to ask contributors to make changes.

Feat

This PR adds a parameter to set the version of the serverless framework CLI to be installed. A new unit test was added to verify the install version.

Fix

This PR also includes a small fix for an issue encountered during testing. No Cloud Provider is needed to simply install the CLI, so in testing the provider was set to a blank string (which is a valid enum). This selection had not yet been accounted for. Added a simple echo statement to show that no option was selected rather than error.

[orb-publisher]

Your development orb has been published. It will expire in 30 days.
You can preview what this will look like on the CircleCI Orb Registry at the following link:
https://circleci.com/developer/orbs/orb/circleci/serverless-framework?version=dev:ca182e676e7901b4234d19fa171d97a7fba4e47b

[KyleTryon]

In testing, attempting to download version 2.72.3, the binary appeared to be downloaded but --version showed 2.72.2. Testing again with version3.15.0

[orb-publisher]

Your development orb has been published. It will expire in 30 days.
You can preview what this will look like on the CircleCI Orb Registry at the following link:
https://circleci.com/developer/orbs/orb/circleci/serverless-framework?version=dev:026d3eba87b0ab624fc20610d49873f6bb8cf55b

[EricRibeiro]

LGTM

[orb-publisher]

Your development orb has been published. It will expire in 30 days.
You can preview what this will look like on the CircleCI Orb Registry at the following link:
https://circleci.com/developer/orbs/orb/circleci/serverless-framework?version=dev:266132eb8e02586e583671e188c0c4d0423e3c2c