add plugin methods to manage the lifecycle of service templates

[swaroopar]

When service templates are registered or updated, we must allow CSP plugins to automate checks wherever necessary.

Method - validateServiceTemplate

• Add interface method -> validateServiceTemplate -> Returns an enum -> APPROVED, MANUAL_REVIEW_REQUIRED, REJECTED
• 'auto-approve' flag validation must move to the corresponding plugin method.
• 'MANUAL_REVIEW_REQUIRED' means the CSP must then review it once manually.
• The default implementation for now can be -> if auto-approve is true, return APPROVED; otherwise return MANUAL_REVIEW_REQUIRED.

Method - prepareServiceTemplate

• Add interface method -> prepareServiceTemplate -> returns void. This method will then run necessary preparation steps in the CSP's infrastructure (Eg., configure API GW, configure IAM, etc)
• When the validateServiceTemplate returns APPROVED or the CSP's review method approve's the service, then call the prepareServiceTemplate in the corresponding plugin.
• Default implementation just returns.

[baixinsui]

I will take it