Increase default number of RMMDIIS iterations to 5

Description

Tests for various systems have shown that number of iterations are generally smaller for 5 RMMDIIS iterations and also the total time is smaller (although each iteration is slightly more costly). This increases the memory needed by RMMDIIS, but should be still moderate enough.

News snippet

Increase default number of RMMDIIS iterations to 5

Checklist

• I have checked that my code follows the Octopus coding standards