fix: Treats mcc and mnc as text instead of numbers

[gruyaume]

Description

The network slice creation modal use to consider MCC's and MNC's starting with zero's as invalid. This PR fixes this problem by considering those entries as text instead of numbers.

Fixes #196

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that validate the behaviour of the software.
• I validated that new and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

[patriciareinoso]

i don't see any validation about the characters that can be used over the mcc and mnc. What happens if we make mcc=abc ?

[gruyaume]

i don't see any validation about the characters that can be used over the mcc and mnc. What happens if we make mcc=abc ?

Agreed, fixed