Add exclude_files

[fujiwara]

ecrm reads exclude_files in config from local files.

exclude_files:
  - path/to/exclude.txt

Exclude file is a text file that includes ECR image URL lines delimited by LF. These images are not deleted by ecrm delete.

# this is a comment
0123456789012.dkr.ecr.ap-northeast-1.amazonaws.com/xxx/yyy:foo
0123456789012.dkr.ecr.ap-northeast-1.amazonaws.com/xxx/yyy:bar
# 0123456789012.dkr.ecr.ap-northeast-1.amazonaws.com/xxx/yyy:baz  # ignored