Add command to wait for open proving window

[travisperson]

Checklist

• This is not a new feature or an enhancement to the Filecoin protocol. If it is, please open an FIP issue.
• This is not brainstorming ideas. If you have an idea you'd like to discuss, please open a new discussion on the lotus forum and select the category as Ideas.
• I have a specific, actionable, and well motivated feature request to propose.

Lotus component

lotus miner - proving(WindowPoSt)

What is the motivation behind this feature request? Is your feature request related to a problem? Please describe.

Restarting a lotus miner during a proving window isn't a good idea. There doesn't appear to be a way to easily determine if a lotus miner is in the middle of a proving window or if a proving window is in the immediate future. Restarting a miner while a windowed post is in flight, or immediately after, before it has landed on chain doesn't seem like a good idea.

Context: #6874

Describe the solution you'd like

This can be a command under lotus-miner proving or in lotus-shed.

We should provide a command that hangs till the open window is closed and it's safe to restart both the daemon and the miner. This also includes not returning if a window is opening soon and work will need to be done in the immediate future.

This could have some nice features along side it. For example the user could query and ask for n consecutive window (eg; needs 60 or 120 minutes to do maintenance). If no window can be found to satisfy this time requirement, the command should error.

The ux / options are open for discussion.

Describe alternatives you've considered

No response

Additional context

No response