Make purification_type string and change numerical values

[lmpawan10]

The following changes have been made:

Inside HardwareMonitor.h

• purification_type declared as string

Inside HardwareMonitor.cc

• 2002: "R1_Single_X-R1_Single_Z"
• 3003: "R1_Single_X-R2_Single_Z"
• 1001: "R1_Single_XZ"
• 1221: "R1_Single_XZ-R2_Single_ZX"
• 1011: "R1_Double_X"
• 1021: "R1_Double_X-R2_Double_Z"
• 1031: "R1_Double_XZ-R2_Double_ZX"
• 1061: "R1_Double_X_Single_Z-R2_Double_Z_Single_X"
• 5555: "CR1_Double_X-CR2_Double_ZX--R1_Single_X-R2_Single_Z"
• 5556: "CR1_Double_X-R1_Single_Z-R2_Single_X"

Here, R1/R2 is for specifying the number of rounds. i.e, R1: Round 1, R2: Round 2

"CR1_Double_X-CR2_Double_ZX--R1_Single_X-R2_Single_Z" states that, Double_X and Double_ZX purification run in Round1 and Round2 respectively only once. Then, Single_X and Single_Z purification run during Round1 and Round2 respectively and repeat for more rounds if needed.

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This change is 

[lmpawan10]

@Naphann

what does 2 in 2002: 2N_ALTERNATE_SINGLE_X_WITH_SINGLE_Z mean?

For 5555,

In the first round, I will change DOUBLE_SELECTION_ZX_PURIFICATION to DOUBLE_SELECTION_Z_PURIFICATION.