Implement setEmergencyShutdown

[MickdeGraaf]

User Story

• As an <audience/user>: PieVault admin
• I want to <action/task>: be able to trigger an emergency shutdown
• so that <outcome/goal/benefit>: To limit losses in case of emergency

Type

• Enhancement
• Maintenance
• Refactor

Description

In case of emergency a PieVault admin should be able to trigger an emergency shutdown which:

• Disables minting. (Can be done by setting the cap to 0)
• Disables adding of new strategies
• Sets the debt ratio of all strategies to 0

Definition of Done

• Implement setEmergencyShutdown
• Unit test setEmergencyShutdown

See Yearn implementation
Part of #30