Settings_Engine: Add LoadSettings method for loading a single settings file

[FraserGreenroyd]

Fixes #3299

[FraserGreenroyd]

@BHoMBot check compliance

[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

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[FraserGreenroyd]

@BHoMBot check versioning
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[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

• check versioning
• check core
• check serialisation
• check null-handling
• check installer

[FraserGreenroyd]

@BHoMBot this is a DevOps instruction. I am requesting neutral checks on: unit-tests

[bhombot-ci]

@FraserGreenroyd I have provided neutral checks to the checks requested. These checks will need to be run properly to obtain full results.

[Tom-Kingstone]

Useful for when we want to load settings for toolkits easily. Approved.

[FraserGreenroyd]

@BHoMBot check ready-to-merge

[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

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There are 18 requests in the queue ahead of you.