Feat: Allow basic parameters to be late bound

[RikudouSage]

Description

This PR allows the three mandatory parameters to be passed as Stringable objects. Those can be used anywhere a string is expected. The advantage is that the __toString() can be resolved at the time of casting to whatever is necessary, like dynamic environment variable.

Relates to Unleash/unleash-client-symfony#66

Type of change

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

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• Unit tests

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[sighphyre]

That's pretty cool actually

LGTM