Skip Pulumi CLI download if runner version satisfies requested CLI version

[ehafenmaier]

Accidentally closed PR #837 when syncing fork.

Original PR

• Add functionality to check GitHub runner for the existence of the Pulumi CLI.
• If the CLI is already installed on the runner check if the runner CLI version matches the requested version from the action input.
• If runner CLI version matches, skip downloading CLI.
• If CLI not installed on runner or runner CLI does not match requested version, proceed to download CLI

NOTE: Skipping the CLI download will also skip the outbound network call in the getVersionObject() method, which was mentioned in #674

This resolves #789