Converted to mod, using jsonpb to marshal stub responses and fixed tests

[HairyMike]

I've updated the master branch on my fork with these changes:
https://github.com/hairymike/gripmock

And created a docker image:
https://hub.docker.com/r/hairymike/gripmock

docker pull hairymike/gripmock

First of all, great work on gripmock!

It would be great to start upgrading some of the other libraries in gripmock. This PR would lay some of the groundwork for this by first changing over go modules, and replacing packr2 with pkger.

There was a problem running go mod init when using packr2, so I went ahead and migrated it.

Included in this PR:

• switched over to go modules
• replaced packr2 with pkger
• fixes to address the well_known_type test failure. The cause of the issue was that the keyword type was making it into an import alias in the server.tmpl file.
• migrated from depreciated protoc plugin lib to protogen
• use jsonpb to marshal stubs to response messages

Few issues that this might resolve:
#61
#58
#51

[jekiapp]

Thankyou for this well written PR 👍 . Sorry for the late response, I will try to find a time this week to detailed check of this PR.

[jekiapp]

In the main() @generator.go, what you want to introduce there?
what is the benefit of using pluginpb.codeGeneratorRequest instead of generator.Request?

does the old lib is deprecated? because the updated code seems less simplistic than previous one.

[jekiapp]

previously we have this one line gen.CommandLineParameters(gen.Request.GetParameter()) and now we had to manually parse the parameter, care to elaborate?

[HairyMike]

I agree,

The reason for the change is that the original generator lib is deprecated, and is not covered by the protocol buffer compatibility guarantee anymore (more details here).

I think there may have been some issue using generator with protogen as well (I can't remember). I'm happy to have a look at backing this part out if its a deal breaker

Thanks for having a look at my PR :)

[jekiapp]

Thankyou for your detailed explanation. PR accepted :)