API to clean up not decryptable saved objects

[lucabelluccini]

Describe the feature:

There are few cases where saved objects should be cleaned up from the Kibana indices.

Saved Objects which cannot be decrypted due to the fact the key has been lost or was not explicitly set (consequence of #81511).

The API should ask for confirmation as there is data loss.
I wouldn't do this automatically as a user might have the encryption key and is just adding the key to the rotation keys.

Describe a specific use case for the feature:

A user created encrypted saved objects on 7.11 with the auto-generated encryption key.
On 7.12, we stop generating it and the user might no more be able to read those objects.
There will be objects kept in Kibana indices which cannot be recovered anymore and those can affect saved object migrations or in any case increase the size of Kibana index.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)