Use XIOS write initial condition functionality in IO_demo

[Nathan Mannall (NMannall)]

PR Summary

Sci/Tech Reviewer:
Code Reviewer:

This PR enables the I/O demo application to write out field data at timestep 0 (i.e. the initial condition of the simulation). The implementation requires XIOS version 3.0.4.1 or greater to use the write_initial_condition file attribute.

The main changes include:

• A new initial_step function to write out the diffusion_field at timestep 0 before the clock is ticked.
• A new write_initial_condition member variable for lfric_xios_file with default value true
• When the I/O is advanced, fields are now sent at the first clock step (i.e. timestep 0)

For a given field, if write_initial_condition = false, this implementation relies on XIOS to prevent data from being sent at timestep 0 using the xios_field_is_active function.

Related to #399

Code Quality Checklist

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trac.log

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Code Review

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