Option to use files for in|exclusion patterns to fix "Error: command too long"

[ilya-lesikov]

We only could include/exclude files from backup by passing them to the
restic binary as an option inline in restic_repos.command.
When the number of in/exclude patterns grows, executed command in cron file
truncated at 999th symbol with error message "Error: command too long":
https://serverfault.com/questions/546342/crontab-maximum-command-length/736010#736010

This PR allows specifying include/exclude files with their contents in
defaults/main.yml, then these files will be created in tasks/install.yml.
Then you can reference these files in your restic_repos.command like this:

restic --files-from {{ restic_config_path }}/includes \
  --exclude-file {{ restic_config_path }}/excludes backup

It will make the command executed by cron daemon much shorter thus avoiding
999 symbols problem.