Drop old cli flags

[vektah]

Removes all of the poorly named flags (eg package, modelPackage and exec) that now live in config, and switch to urvaf/cli to remove all the nasty global state in flag parsing.

gqlgen help
NAME:
   gqlgen - generate a graphql server based on schema

USAGE:
   gqlgen [global options] command [command options] [arguments...]

DESCRIPTION:
   This is a library for quickly creating strictly typed graphql servers in golang. See https://gqlgen.com/ for a getting started guide.

COMMANDS:
     generate  generate a graphql server based on schema
     init      create a new gqlgen project
     help, h   Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --verbose, -v             show logs
   --config value, -c value  the config filename
   --help, -h                show help

init has a few extra knobs that were being conflated with gen

$ gqlgen help init
NAME:
   gqlgen generate - generate a graphql server based on schema

USAGE:
   gqlgen generate [command options] [arguments...]

OPTIONS:
   --verbose, -v             show logs
   --config value, -c value  the config filename
   
roci :: 99designs/gqlgen » gqlgen init -h    
NAME:
   gqlgen init - create a new gqlgen project

USAGE:
   gqlgen init [command options] [arguments...]

OPTIONS:
   --verbose, -v             show logs
   --config value, -c value  the config filename
   --server value            where to write the server stub to (default: "server/server.go")
   --schema value            where to write the schema stub to (default: "schema.graphql")

I have:

• Added tests covering the bug / feature (see testing) - already covered
• Updated any relevant documentation (see docs) - already covered

[creativej]

Looks good it's definitely much simpler and easier to read.
This looks like it deletes the cmd override of specific config values such as exec.files and etc.
Is that because they're not needed anymore?

[vektah]

Yeah, sorry if that wasn't clear from the PR description. All of the config overriding flags are gone.