chore: add import_paths on the configuration file (#2)

[tonicospinelli]

These changes reduce tricks some projects face to get proto import path dependencies when it depends on multiple resources in different paths.

Here is a snippet of how some projects use it:

find api/proto -name '*.proto' -print0 2>/dev/null | xargs -0 --no-run-if-empty -n 1 \
		api-linter --set-exit-status --config .api-linter.yml \
		$(sed -n -e '/roots:/,/:$/{s/^\s*- /-I /p}' buf.yaml)

or

find api/proto -name '*.proto' -print0 2>/dev/null | xargs -0 --no-run-if-empty -n 1 \
		api-linter --set-exit-status --config .api-linter.yml \
		-I import/path1 -I import/path2

Adding import_paths in the configuration file is helpful to centralize the api-linter directives. See:

- include_paths:
    - path_1/**/*.proto
  import_paths:
    - import/path

Using the above config file the command was pretty easy to use:

$ find api/proto -name '*.proto' -print0 2>/dev/null | xargs -0 --no-run-if-empty -n 1 \
		api-linter --set-exit-status --config .api-linter.yml