KNP agent should pick the larger of the two server counts

[konryd]

This way, when agent and server both switch from server-provided counts to counting leases, we will maintain compatibility in both directions:

• response-reliant agent with lease-enabled server: would work, as servers still send down the (static, flag-provided) server count in the response header
• lease-counting agent with non-lease-enabled server: would work, as agent would fall back on the number provided by the servers

Thanks to this compatibility, enabling lease-counting in a fleet of clusters is much more practical (there's no need for two separate, interdependent rollouts).

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[cheftako]

/ok-to-test

[cheftako]

Not sure this is what we want. This clearly works when we are scaling up the number of KNP servers. However I believe this prevents us from easily scaling down the number of KNP servers. I thought was one of the goals of the lease system.

[konryd]

That depends on how the static --server-count flag is set. With these changes it can:

• be set to 1 to rely on leases alone
• be set to some-default-value to provide a lower bound as a safety

The default lower bound is critical when we're gradually replacing agents and servers in parallel:
We will still have a portion of the servers not recording their lease and a portion of agents assuming too-low count (because they only look at leases).

[cheftako]

Golang does not do fall through (https://go.dev/ref/spec#Expression_switches "the first one that equals the switch expression triggers execution of the statements of the associated case; the other cases are skipped") So I believe empty string is going to silently do nothing, which I don't think is what we want.

Did you mean the following?
case "", "default":

[konryd]

Thanks! Fixed.

[cheftako]

/lgtm
/approve

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This pull-request has been approved by: cheftako, konryd

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