kvserver: use WithExplicitX for snapshot rate limits

[tbg]

Is your feature request related to a problem? Please describe.

A customer (internal) accidentally set the snapshot rate limits to 8, which is 8 bytes per second. They intended to set it to 8mb/s.

Describe the solution you'd like

Use the equivalent of

cockroach/pkg/settings/duration.go

Lines 155 to 160 in 30afca0

	// RegisterPublicDurationSettingWithExplicitUnit defines a new
	// public setting with type duration which requires an explicit unit when being
	// set.
	func RegisterPublicDurationSettingWithExplicitUnit(
	class Class, key, desc string, defaultValue time.Duration, validateFn func(time.Duration) error,
	) *DurationSettingWithExplicitUnit {

for all of our cluster settings for which it makes sense.

Note that this isn't a backwards-compatible change, but we should make it regardless.

Jira issue: CRDB-12806

[tbg]

This is somewhat awkward: for each setting type that we want this for, we need to implement a new type and special case it here:

cockroach/pkg/sql/set_cluster_setting.go

Lines 157 to 162 in 6700a17

	case *settings.DurationSettingWithExplicitUnit:
	requiredType = types.Interval
	// Ensure that the expression contains a unit (i.e can't be a float)
	_, err := p.analyzeExpr(
	ctx, expr, nil, dummyHelper, types.Float, false, "SET CLUSTER SETTING "+name,
	)

I was hoping we could "just" have an .WithExplicitUnit() chainer but it's not as easy.

Since we already set min values for these rate limits, I am not convinced we should be doing more this time around.

It does seem desirable to have better settings infra though, where units can be requested for any setting without doing plumbing in the SQL layer.

cc @mwang1026 not sure where to route this ask.

[mwang1026]

I think given Nathan's min setting change we're OK to close this for now. re: cluster setting infra let's take that offline