Apply the protobuf gradle plugin properly

[SerialVelocity]

We exclude files that don't exist currently. Should we delete the proto or generate the files?

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This change is 

[codecov-io]

Current coverage is 53.52% (diff: 100%)

Merging #1384 into develop will increase coverage by 0.65%

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[jboreiko]

Looks good, just don't really have a handle on where or how these things are used yet so going to wait on finding out more.

[jboreiko]

this package (and the leader-election-api-protobuf) are a bit odd in general considering they only exist to contain generated code. I'm wondering if we should just throw it all into there source. I've reached out to @gbonik hoping to find out more about who actually consumes these.

[jboreiko]

Cool, just caught up with @rjullman, after poking around. It looks like several of these should only exist internally (where the generated code actually lives). I'll amend the PR to remove them and the excludes for them as well. I will also be filing a ticket for OSS the protobuf based timestamp and lock services (which these use). These protos already exist internally, this simply removes some duplication.

[jboreiko]

Could clean up the gradle a bit (version strings maybe?) but seems fine and isn't likely to be touched anytime soon.

[jboreiko]

#1449