Prepare for release v1.2.0

[airwoodix]

Summary

Bump package version and freeze changelog for release v1.2.0.

[wilfried-huss]

I don't know if this problem is now, but there is a problem with the encoding in the Windows tests:

C:\Users\runneradmin\AppData\Local\pypoetry\Cache\virtualenvs\qiskit-aqt-provider-gPSaTfai-py3.10\lib\site-packages\qiskit\visualization\circuit\text.py:787: RuntimeWarning: The encoding cp1252 has a limited charset. Consider a different encoding in your environment. UTF-8 is being used instead
  warn(
Traceback (most recent call last):
  File "D:\a\qiskit-aqt-provider\qiskit-aqt-provider\examples\quickstart-transpile.py", line 30, in <module>
    print(transpiled_circuit)
  File "C:\hostedtoolcache\windows\Python\3.10.11\x64\lib\encodings\cp1252.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode characters in position 30-60: character maps to <undefined>

[airwoodix]

I saw this when working on #123. It appears when printing a qiskit QuantumCircuit instance. I don't know how to fix that but also didn't invest much time in it because it's not critical (actual errors would still fail the CI step).