Feature: Add a --version flag to aid in debugging

[nicholasyager]

Description and motivation

As mentioned in #198, there is a distinct need to have a --version flag added to dbt-meshify to make it easier for users to identify which version of dbt-meshify they have installed. This PR adds this functionality, such that running dbt-meshify --version will print the current version number from the package information (as stored w/in the internals of python), and exit.

To accomplish this, I added the new option, and then added the invoke_without_command=True argument to click.group() to allow us to run code in the cli group when a command has not been provided. I then manually implemented a default check to print help text if a subcommand has not been provided.

Resolves: #200

Examples

$ dbt-meshify --version
0.5.2                 

$ dbt-meshify
Usage: dbt-meshify [OPTIONS] COMMAND [ARGS]...

Options:
  --dry-run
  --debug
  --version  Show version information and exit
  --help     Show this message and exit.

Commands:
  connect    Connects multiple dbt projects together by adding all...
  group      Creates a new dbt group based on the selection syntax...
  operation  Set of subcommands for performing mesh operations on dbt...
  split      Splits out a new subproject from a dbt project by adding all...
  version    Increment the models to the next version, and create in the...          

[dave-connors-3]

is this an intentional inclusion of result on this line?

[nicholasyager]

Nope! I'll fix that.

[dave-connors-3]

pending comment on the test, but looks good otherwise!