Add required argument to initialize Span

[ahlaw]

Description

Adding a parameter to SDK Span constructor. An additional argument is now required to call the Span constructor, else an Exception is raised. This is to discourage callers from creating Spans directly.

Fixes #1000

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Unit test to verify an exception will be thrown when the constructor is called without the additional argument
• Tox suite to check no existing functionality has been broken

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added