feat: add release version and release date to threat models and printed report coversheet

[praxzy]

Summary:

closes #1621

I have added release version and release date fields to threat models that are now exported to the PDF report.
The previous "Date Generated" is now replaced with "Release Date".
The release date falls back to the generated date if no date is provided.

Description for the changelog:

add release version and release date fields to threat models and printed report coversheet

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[praxzy]

Hey @jgadsden

Please let me know if this implementation looks good :)

[jgadsden]

thanks for the pull request @praxzy , apologies from my long delay before replying (we are all volunteers and sometimes volunteering is a luxury that is hard to fit round paid-for and family)

Could you update the schema ? td.vue/src/assets/schema/threat-dragon-v2.schema.json for these new keys?
all should be good after that

[praxzy]

done!