Improve error on trying to create more than max allowed Schedule PEPs

Why are we doing this work

• users want an obvious explanation of why they cannot create another Schedule PEP

Relevant links

Current	Proposed
	TBD

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

• backend / frontend if a scheduled PEP is already created, disable the option to create a new one with a tooltip referencing the max amount
• backend modify the message to be more readable

Verification steps