Add mandatory flag --upgrade-height to hermes upgrade client

[plafer]

Summary

Add --upgrade-height to hermes upgrade client and have hermes wait for that height until it submits the transaction.

Also document that hermes upgrade client must be run when the chain is halted if no --upgrade-height is included for the command to succeed.

Problem Definition

Currently hermes upgrade client needs to be run when the chain is halted for the command to succeed, and the error message is confusing when you don't.

We could add an optional flag --upgrade-height (or --halt-height?) and have hermes wait for that height until it submits the transaction. This would make it less confusing for users, as it is currently unclear that the command needs to be run when the chain is halted.

Acceptance Criteria

• The --upgrade-height (or similar name) option is added to hermes upgrade client
• Document that the command must be run when the chain is halted if --upgrade-height is not specified

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[plafer]

See #2304 for suggestion to force users to include an upgrade height with this command.

EDIT: We should really make this flag mandatory, see PR comment