Update TTL coefficient levels

Currently, TTL coefficients can be

• randomly drawn in a uniform distribution [-2.3, 2.3] mm/rad at the beginning of the simulation
• set to fixed values, randomly picked in the same distribution once and for all
• set to user-defined values

According to issue 2 of Ewan’s stop model (LISA-UKOB-INST-ML-0001-i2 LISA TTL STOP Model.xlsx, Summary table), the TX total TTL coefficients is now estimated to be 2.4 mm/rad, and for the RX 2.2mm/rad.

We should update the random distributions and draw new values for the fixed values.

@mastaa @swetashah @guwann @jslutsky