Replace oracle managed keys with vault(custom) keys

we will encrypt block volume oracle managed keys with our vault keys that we have already created.

1. Open block volume details page and click on the option Assign next to Encryption key

2. Select created vault & vault key and click on assign

3. Now, vault key has assigned to block volume.

Note: We successfully assigned the Vault Key (Custom Key) to the Block Volume without creating any new policies. This is because the required policy (Allow service blockstorage to use keys) was already created during the Boot Volume configuration.

Since both Boot Volumes and Block Volumes are part of the same Block Storage service backend in OCI, a single policy covers both. A new policy will only be required when we assign Custom Keys to a different service, such as Object Storage (Buckets).