Add PhaseShift transform

[guarin]

See #1646 for information

[4ritam]

Hi, I am new to open source contributions, I would like to contribute to this one. Tell me if I am doing it right.

[guarin]

Hi, thanks a lot for helping out! Let me know if you need any help :)

[JanumalaAkhilendra]

Hi, if this issue is still open, I would like to work on it. Please assign it to me .

[4ritam]

@JanumalaAkhilendra you can take it if you want. I tried and didn't understand much. @guarin can you please assign him.

[SauravMaheshkar]

Hi, if this issue is still open, I would like to work on it. Please assign it to me .

I've assigned the issue to you @JanumalaAkhilendra, looking forward to the PR.

[pearguacamole]

@guarin Hi, I'd like to work on this issue, could you assign it to me also

[SauravMaheshkar]

@pearguacamole, we only allow one assignment per issue; please have a look at the other available issues: good first issue

[pearguacamole]

Sure I'll look into other other available issues, do assign me this If it becomes available

[guarin]

For context, you have to do pretty much the same thing as in #1694 but instead of changing the amplitude you have to modify the phase.

[guarin]

@JanumalaAkhilendra did you already have time to look into this?

[JanumalaAkhilendra]

@guarin it is taking more time than i expected to complete this, you can assign it to the next person

[guarin]

@pearguacamole this issue would be free again if you are still interested in working on it. You can follow the structure from this PR #1694 but instead of modifying the amplitude you have to modify the phase.

[pearguacamole]

Yes, I'm interested in working on it, you can assign it to me. Thanks

[pearguacamole]

@guarin sorry for the delay, got some impromptu exams. So, I basically did the same thing as #1694 but added a step to decide if we are going to add or subtract theta while shifting the phase, as suggested by the paper.
Here I have used Bernoulli distribution of 0.5 to determine the sign of theta, as there was no indication of basis to decide the sign in the paper.
Please do suggest any changes you think should be made. Thanks