Support sha256 on Postgresql 10+

[pmav99]

Postgresql 10+ supports scram-sha256 hashing for passwords. The inspect check though only allows md5.
More info here: https://paquier.xyz/postgresql-2/postgres-10-scram-authentication/

postgres-baseline/controls/postgres_spec.rb

Lines 259 to 271 in 01175b7

	control 'postgres-13' do
	impact 1.0
	title 'Require MD5 for ALL users, peers in pg_hba.conf'
	desc 'Require MD5 for ALL users, peers in pg_hba.conf and do not allow untrusted authentication methods.'
	describe file(POSTGRES_HBA_CONF_FILE) do
	its('content') { should match(/local\s.*?all\s.*?all\s.*?md5/) }
	its('content') { should match(%r{host\s.*?all\s.*?all\s.*?127.0.0.1\/32\s.*?md5}) }
	its('content') { should match(%r{host\s.*?all\s.*?all\s.*?::1\/128\s.*?md5}) }
	its('content') { should_not match(/.*password/) }
	its('content') { should_not match(/.*trust/) }
	its('content') { should_not match(/.*crypt/) }
	end
	end

[chris-rock]

@pmav99 Thank you for raising the issue. As discussed in #23 we should collect the improvements for Postgres 10 and add improvements via PRs to support that.