Refactor DatabaseConnection to use DatabaseConfiguration

.rubocop_todo/rspec/named_subject.yml

.rubocop_todo/style/inline_disable_annotation.yml

Gemfile

gems/gitlab-backup-cli/lib/gitlab/backup/cli.rb

gems/gitlab-backup-cli/lib/gitlab/backup/cli/utils.rb

.../gitlab-backup-cli/lib/gitlab/backup/cli/utils/pg_dump.rb

gems/gitlab-backup-cli/sig/gitlab/backup/cli.rbs

...gitlab-backup-cli/sig/gitlab/backup/cli/utils/pg_dump.rbs

...b-backup-cli/spec/gitlab/backup/cli/utils/pg_dump_spec.rb

lib/backup/database.rb

lib/backup/database_configuration.rb

lib/backup/database_connection.rb

lib/backup/database_model.rb

lib/backup/dump/postgres.rb

spec/lib/backup/database_configuration_spec.rb

spec/lib/backup/database_connection_spec.rb

spec/lib/backup/database_model_spec.rb

spec/lib/backup/database_spec.rb

spec/lib/backup/dump/postgres_spec.rb