Add support for predefined variations

[z4kn4fein]

Describe the purpose of your pull request

• Updated the flag-v2 create command to accept predefined variations with initial values.
• Added flag-v2 variation command for managing the predefined variations of a flag.

Related issues (only if applicable)

• https://trello.com/c/ExyI3v0t/31-cli

Security (only if applicable)

• n/a

Requirement checklist (only if applicable)

• I have covered the applied changes with automated tests.
• I have executed the full automated test set against my changes.
• I have validated my changes against all supported platform versions.
• I have read and accepted the contribution agreement.