Add converter to make sure we have a string value when expect it

Breaking change

Proposed change

Add converters that returns null if expected string value is not a string when deserializing devices or the string if it is a valid string.

Type of change

[ ] Dependency upgrade
[x] Bugfix (non-breaking change which fixes an issue)
[ ] New feature (which adds functionality to an existing integration)
[ ] Breaking change (fix/feature causing existing functionality to break)
[ ] Code quality improvements to existing code or addition of tests

Additional information

This PR fixes or closes issue: fixes #1125
Link to documentation pull request:

Checklist

[x] The code change is tested and works locally.
[x] Local tests pass. Your PR cannot be merged unless tests pass
[x] The code compiles without warnings (code quality check)
[x] Tests have been added to verify that the new code works.

If user exposed functionality or configuration are added/changed:

[ ] Documentation added/updated for http://netdaemon.xtz

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81%. Comparing base (7f9914e) to head (9fb54cc).

Files	Patch %	Lines
....HassClient/Internal/Json/EnsureStringConverter.cs	60%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1126 +/- ## ==================================== - Coverage 81% 81% -1% ==================================== Files 189 190 +1 Lines 3838 3843 +5 Branches 460 462 +2 ==================================== + Hits 3141 3144 +3 - Misses 517 518 +1 - Partials 180 181 +1 ``` | [Flag](https://app.codecov.io/gh/net-daemon/netdaemon/pull/1126/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=net-daemon) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/net-daemon/netdaemon/pull/1126/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=net-daemon) | `81% <60%> (-1%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=net-daemon#carryforward-flags-in-the-pull-request-comment) to find out more.

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net-daemon / netdaemon