Allow configuration of gem

[mrtnin]

Currently, the Backy gem lacks the ability to be easily configured with different database connection settings. This issue aims to address this limitation by allowing the gem to take the database connection information either directly from Rails or through custom configuration.

• Update the gem to automatically detect and use the Rails database configuration settings if no custom configuration is provided.
• Modify the gem to prioritize using custom configuration settings if they are present, and fall back to using Rails configuration settings if custom settings are not available.

Example initializer in a Rails app:

Backy.configure do |config|
  config.adapter = :psql
  config.storage = :s3
  config.app_name = "flytaxi"
  config.environment = Rails.env
  config.s3_bucket = "flytaxi-backups"
  config.s3_region = "eu-central-1"
  config.s3_access_key_id = ENV["AWS_ACCESS_KEY_ID"]
  config.s3_secret_access_key = ENV["AWS_SECRET_ACCESS_KEY"]
  config.s3_endpoint = "https://s3.eu-central-1.amazonaws.com"
end