Add manage invites endpoints

[PeterOcansey]

resolves #https://github.com/mailersend/mailersend/issues/6071

Changelist

• [x] Add list invite endpoint
• [x] Add find invite endpoint
• [x] Add resend invite endpoint
• [x] Add cancel invite endpiont

[JoaoFSCruz]

@PeterOcansey I think we can release this, right?

[PeterOcansey]

@JoaoFSCruz I missed out README, I just updated it now....let me know if ok to release