Tests for key manager upgrades

[kostko]

Depends on #2516.

We should add E2E tests for key manager runtime upgrades (without production keys).

The process of upgrading the KM is the following:

• First make sure an initial key manager is registered and operational.
• Build an upgraded key manager runtime enclave (anything which changes MRENCLAVE should be fine).
• Update the key manager policy to include the MRENCLAVE for the new runtime and wait for the policy to propagate.
• Leave old key manager nodes running.
• Spin up new key manager nodes with upgraded enclave.
• Wait for the key manager nodes to replicate the master secret.
• Verify that the key manager nodes work.
• Take down old key manager nodes.
• Verify that the key manager nodes work.