CI: improve rate switching testing in long sanitizer tests

The long sanitizer tests rely on scripts/config/ivas_modes.json for parametrization of the specific modes. For rate switching modes, a rate switching pattern is set for each mode/bandwidth combination like so:

"bitrates": {
                 "wb": {
                     "all": "{sw_files_path}/sw_13k2_512k.bin"
                 },
                 "swb": {
                     "all": "{sw_files_path}/sw_13k2_512k.bin"
                 },
                 "fb": {
                     "all": "{sw_files_path}/sw_13k2_512k.bin"
                 }
             }

For testing, it would be better to vary the bitrate switching patterns as sometimes bugs depend on the starting bitrate. Also, there are specially engineered patterns e.g. for OMASA and MC that trigger all critical technology transitions. Goal is to add functionality to dynamically change the br switching patterns in each ltv sanitizer test run so that all operating points get tested with all critical switching patterns regularly.