(BE) Workspace Invitation

[devleejb]

What would you like to be added:
Implement the workspace invitation logic with the following features:

• Invite users using a distinguishing token (email, ID, etc.).
  • Alternatively, provide an invitation link.
• Invited users have the option to accept or decline the invitation.

The specific implementation should be discussed in #17.

Why is this needed:

• To provide workspace feature

Additional Information:

[devleejb]

Implement invitation logic via URL sharing.

Following APIs are required.

• Generate JWT Token
• Join Workspace via JWT Token