feat: improve output formatting when running run custom_lint

[alestiago]

Description

As a developer I would like the output of custom lint to be beautiful and informative just like dart analyze.

I would like:

1. Running flutter pub run custom_lint to include a summary documenting the total number of issues found (just like dart analyze)
2. Running flutter pub run custom lint to show a colourful and well indented output (just like dart analyze).
3. Running flutter pub run custom lint to show a well formatted time output of the total execution time (just like dart analyze).

Output comparison screenshots

Example dart analyze output

Example flutter pub run custom lint output

[kuhnroyal]

I already added a PR for this, please give it a try.

[yamarkz]

@kuhnroyal @rrousselGit

I look forward to your contribution.
Will it be possible to change the output with the --fatal-infos and --no-fatal-infos options of dart analyze?
I want to have good control over execution and errors in CI.

[rrousselGit]

That's a separate issue.