Fix Random-Midpoint-Displacement algorithm

[RShaw026]

Description and Context

In this MR, a variable, the initial standard deviation for the RMD algorithm, is added as an input parameter. Earlier, this variable was hard-coded, so we could not completely define a rough surface with the available input parameters. The empirical relation to choose these parameters w.r.t. the statistical parameters are given in the following article: On the reliability of microscopical contact models.

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How Has This Been Tested?

The generated topology with the given parameters is compared with the MATLAB code.

Checklist

• [ ] My commit messages mention the appropriate GitHub issue numbers and are longer than one line where appropriate.
• [x] I have added/updated documentation where necessary.

Additional Information

Interested Parties / Possible Reviewers

@mayrmt @NoraHagmeyer @jacopenji

[RShaw026]

@mayrmt Jacopo and I discussed your comment, and we thought of changing the variable name to initial_topology_std_deviation to avoid any confusion.