Don't block hosts for potentially temporary issues

[n8mgr]

This is something we added to indexd that in hindsight is probably too aggressive. These hosts shouldn't be considered for new contracts or renewals and goodForUpload: false, but they should be able to be used again provided they eventually "fix" the issue. A large portion of the sector migrations came from hosts that were blocked due to a usability issue, but can now be unblocked.

This does complicate migrations. We will need to decide on when to migrate existing data, especially if we decide to immediately treat the hosts as unusable for external apps.

Basically anything in here should no longer be considered a permanent offense:

// FailedChecks returns a string representing all failed Usability checks.
func (u Usability) FailedChecks() []string {
	var reasons []string
	if !u.Uptime {
		reasons = append(reasons, "Uptime")
	}
	if !u.MaxContractDuration {
		reasons = append(reasons, "MaxContractDuration")
	}
	if !u.MaxCollateral {
		reasons = append(reasons, "MaxCollateral")
	}
	if !u.ProtocolVersion {
		reasons = append(reasons, "ProtocolVersion")
	}
	if !u.PriceValidity {
		reasons = append(reasons, "PriceValidity")
	}
	if !u.AcceptingContracts {
		reasons = append(reasons, "AcceptingContracts")
	}
	if !u.ContractPrice {
		reasons = append(reasons, "ContractPrice")
	}
	if !u.Collateral {
		reasons = append(reasons, "Collateral")
	}
	if !u.StoragePrice {
		reasons = append(reasons, "StoragePrice")
	}
	if !u.IngressPrice {
		reasons = append(reasons, "IngressPrice")
	}
	if !u.EgressPrice {
		reasons = append(reasons, "EgressPrice")
	}
	if !u.FreeSectorPrice {
		reasons = append(reasons, "FreeSectorPrice")
	}
	return reasons
}

[ChrisSchinnerl]

So hypothetically we could update BlockHosts to not set host_id = NULL and also avoid setting all of a blocked host's contracts good = FALSE. Then we wouldn't migrate any sectors until MarkUnrenewableContractsBad marks the contracts bad.

If we combine that with automatically unblocking bad hosts assuming that they have been blocked due to usability reasons and not by the user, we might achieve this.

The only issue is not being able to migrate data in time. Half the renew window is not a lot of time for large hosts. We could improve this a bit by updating MarkUnrenewableContractsBad to immediately mark a contract bad that enters its renew window assuming that the host it belongs to is also bad. That gives us 1 week on zeus.

We could also completely detach it from the renew window and use the amount of data a host stores as an indicator. Although that might be counterproductive.

[ChrisSchinnerl]

NOTE: I moved this to Triage to make sure discussions show up in the corresponding project board.