Fix stories that are broken for variants

[Bopchy]

Related to #3183

Overall change: Add selectedService to withServicesKnob storyProps to make it available to stories that use the knob. Adding selectedService to storyProps makes the service selected from the dropdown available in a story, through props, as it appears in the dropdown & TEXT_VARIANTS.

This change will allow work arounds to get TEXT_VARIANTS property values for services with variants to be removed.

Code changes:

• Add selectedService to withServicesKnob storyProps.
• Update tests.

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• I have assigned myself to this PR and the corresponding issues
• Automated jest tests added (for new features) or updated (for existing features)
• This PR requires manual testing

[DenisHdz]

Thanks for the fix 👍

[thekp]

Thanks for the fix Ruth,

Note: psammead-most-read has a little hack that fixes it for variants so after this gets merged we can remove this and update the packages were we need to use this new prop.

[PriyaKR]

The issue cant be tested in this PR.Can be tested when this PR is done #3291