[SIGMON-541] function processing the signal with statuses added

Context

• Task: https://its.cern.ch/jira/browse/SIGMON-541
• In eDSL we have a lot of assertions like that:
  AssertThat(<state>).changesOnceTo(false).starting(2, MILLI(SECOND)).before(<start time>).endingAt(<end time>)
  Now it will be possible to do:

df = SignalProcessing(my_raw_signal).do_stuff().do_stuff().decode_state(<state signal name>, [all interesting states]).get_dataframe()
result = df.loc[<start time>-2000:<end time>, <state>].diff().dropna().sum() == 1

What was done

• a simple processing method added to SignalProcessing

TODO

• ?

QA

• sonar link: https://acc-sonar.app.cern.ch/dashboard?id=lhc-sm-api&branch=SIGMON-541_pc_state_processing_function
• code was tested

Review objectives

• ? assessment of code functionality
• ? assessment of code quality
• ? identifying potential refactorings / logic common to other projects
• ? knowledge sharing
• ? getting help to understand a piece of code

Closes SIGMON-541