[Server] GDS Push: Enable regeneratePrivatekey for CreateSigningRequest method of Server

Proposed changes

Enable the server to generate a new application Certificate Private key when the client requests so in the CreateSigningRequest method.

Related Issues

Fixes #2774

Types of changes

[x] Bugfix (non-breaking change which fixes an issue)
[ ] Enhancement (non-breaking change which adds functionality)
[ ] Test enhancement (non-breaking change to increase test coverage)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
[ ] Documentation Update (if none of the other choices apply)

Checklist

[x] I have read the CONTRIBUTING doc.
[x] I have signed the CLA.
[x] I ran tests locally with my changes, all passed.
[] I fixed all failing tests in the CI pipelines.
[ ] I fixed all introduced issues with CodeQL and LGTM.
[ ] I have added tests that prove my fix is effective or that my feature works and increased code coverage.
[ ] I have added necessary documentation (if appropriate).
[ ] Any dependent changes have been merged and published in downstream modules.

Further comments

Codecov Report

Attention: Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.

Project coverage is 54.72%. Comparing base (3d24c0e) to head (8df3209). Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...a.Server/Configuration/ConfigurationNodeManager.cs	95.23%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2778 +/- ## ========================================== - Coverage 55.11% 54.72% -0.40% ========================================== Files 349 349 Lines 65975 65993 +18 Branches 13534 13539 +5 ========================================== - Hits 36364 36116 -248 - Misses 25738 25952 +214 - Partials 3873 3925 +52 ``` | [Flag](https://app.codecov.io/gh/OPCFoundation/UA-.NETStandard/pull/2778/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OPCFoundation) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/OPCFoundation/UA-.NETStandard/pull/2778/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OPCFoundation) | `?` | | 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=OPCFoundation#carryforward-flags-in-the-pull-request-comment) to find out more.

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OPCFoundation / UA-.NETStandard