[DPE-6160] block charm if password update fails

[reneradoi]

This PR adds functionality to the charmed etcd operator to give feedback to users in case a password update fails. It will set the app and unit status to blocked status if:

• the password cannot be updated in etcd
• the secret has not been granted to the charmed etcd application
• the content of the secret is invalid (username other than root)

[reneradoi]

This PR will stay in draft untill we came to an agreement on how to handle charm status in etcd.