WSTEAMA-1515-added support for routes to have variants at the end

[Nabeel1276]

Resolves (https://jira.dev.bbc.co.uk/browse/WSTEAMA-1514)

Overall changes

Added support for routes with variants such that the variant is at the end of the script. e.g.
Before: /service/variant/topics/id
After: /service/topics/id/variant

Code changes

• Added getVariantTopicPageRegex function which correctly maps the variant to the end of the url as expected.
• Added unit tests to verify that the order of the route is the correct order.
• Added variantTopicPath as a valid path in the array.
• Added testTopics function which ensures error handling and to return a correct response based on the route provided

Testing

• Added unit tests.

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Add Links to useful resources related to this PR if applicable.

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[Nabeel1276]

Apologies for having this all in one commit, I made the changes on latest and then transferred them to a new branch and was having issues with git.

[amoore108]

Nice one!