Make encryptedSavedObjects plugin dependency optional and stop relying on usingEphemeralEncryptionKey

[azasypkin]

As we agreed in #79943 (comment) Monitoring plugin should make encryptedSavedObjects plugin dependency optional (if not done yet) and stop relying on usingEphemeralEncryptionKey setup contract property.

If encryptedSavedObjects dependency is available that would mean that the proper encryption key is set, otherwise dependency won't be available.

NOTE: we can update encryptedSavedObjects plugin behavior only once all consumers stop using usingEphemeralEncryptionKey, we are targeting 7.12 and hence marking all related issues as blocking for that release.

[elasticmachine]

Pinging @elastic/stack-monitoring (Team:Monitoring)

[nreese]

Closing, duplicate of #81619

[azasypkin]

Hey @elastic/stack-monitoring ,

Can you please confirm that you're still targeting 7.12 for this work? Once you merge your part we'll remove usingEphemeralEncryptionKey from the EncryptedSavedObjects plugin contract in #81511.

Thanks!

[chrisronline]

@azasypkin Yes, we can do this for 7.12

[chrisronline]

@azasypkin This is up now: #88884