Deprecate NewClient, create Dial, NewLazyClient, and CheckHealth calls and support laziness

[cretz]

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

Today we have NewClient which, possibly unexpectedly to users, does more than create a client, it also connects to the server to confirm all connectivity. We previously had the ability to disable this but we removed that in #706.

Describe the solution you'd like

• (re)Add client.Options.ConnectionOptions.DisableEagerConnection bool that defaults to false for NewClient
• Add client.Dial call that force-sets client.Options.ConnectionOptions.DisableEagerConnection to false (so basically it's the same as NewClient today)
• Add client.NewLazyClient call that force-sets client.Options.ConnectionOptions.DisableEagerConnection to true
• Deprecate NewClient in favor of the Dial and NewLazyClient calls
• Add a client ensureServerCapabilitiesFetched that atomically lazily obtains the server capabilities if not fetched already and are memoized on success
• Update all client calls to have ensureServerCapabilitiesFetched call to support lazy connectivity
• Add a CheckHealth call on the client that uses the gRPC health API (note, it too will lazily fetch capabilities)

[Spikhalskiy]

This scope supersedes #753 and #595