[FSSDK-8955] Refac: Replaced all instances of full stack except from changelog file and code files

[mnoman09]

Summary

• Updated readme file and matched its format with the provided sample readme file.
• Removed all occurrences of full stack with Optimizely Feature Experimentation

Test plan

All tests should pass.

Issues

• "FSSDK-8955"

[mikechu-optimizely]

I didn't even think about FSC and FXC naming now @jaeopt Good call out

[mikechu-optimizely]

@mnoman09 The linter is not happy with the markdown. Should we disable validation or go ahead and clean based on the rules?

[mikechu-optimizely]

I disabled super-linter's markdown linting. Waiting for FSC to finish successfully.

[mikechu-optimizely]

@mnoman09 Should I go ahead and squash+merge?