fix read_callback user provided input case (in)sensitivity

[realvitya]

Description

This PR is about to handle the situation when user provides input for contains or not_contains with capital letters while case_insensitive attribute only lowers device input's case. Previously, input is not matched though the difference is only letter case. This fix basically lowers user input strings if case_insensitive is True and string in operator will work as intended.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

pytest case added in line with the spirit of the project owner.

Checklist:

• My code follows the style guidelines of this project (no GitHub actions complaints! run make lint before
  committing!)
• I have commented my code, pydocstyle and darglint are happy, docstrings are in google docstring format, and all
  docstrings include a summary, args, returns and raises fields (even if N/A)
• I have added tests that prove my fix is effective or that my feature works, if adding "functional" tests please
  note if there are any considerations for the vrnetlab setup
• New and existing unit tests pass locally with my changes

[carlmontanari]

@realvitya thank you as always!! LGTM!