fixes issues with adding new parts to a subject when creating a CSR

[tylergmuir]

SUMMARY

Fixes an issue where if you include parameters to add to a subject they will not be included if the current certificate does not include them.

Fixes #496

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

purefa_cert

ADDITIONAL INFORMATION

• All new PRs must include a changelog fragment
• Details of naming convention and format can be found here

[CLAassistant]

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