Changing compression mode for ITk digitization in SCT_FrontEnd (ATLITKSW-122)

Investigating the increase in the number of SSS seeds in 21.9 wrt 20.20, we ended up noticing a related increase in the number of SCT RDOs (and clusters). Comparing the configuration of the digitization tools in 21.9 against 20.20 I noticed the usage of a different compression mode. I switched to the same used in 20.20 and the number of SCT RDOs drops, giving a reduction of ~60% in the number of SSS seeds:

Before MR:

| Kind of seed         |     PPP      |     PPS      |     PSS      |     SSS      |     ALL      |
| Input  seeds         |       267188 |            0 |            0 |       148611 |       415799 |

After MR:

| Kind of seed         |     PPP      |     PPS      |     PSS      |     SSS      |     ALL      |
| Input  seeds         |       267188 |            0 |            0 |        57070 |       324258 |

This also provides a reduction in the track finding execution time:

Before MR:

InDetSiSpTrackFinderSLHC:Execute    INFO Time User   : Tot= 81.6  [s] Ave/Min/Max= 8.16(+- 2.45)/ 4.77/ 13.3  [s] #= 10

After MR:

InDetSiSpTrackFinderSLHC:Execute    INFO Time User   : Tot=   47  [s] Ave/Min/Max=  4.7(+- 1.38)/ 2.92/ 7.59  [s] #= 10

Changes are minimal in the efficiency.