Refactor text endpoint

[StephenCathcart]

Description 🤔

"As a developer, I want to revert to Spring MVC from Spring WebFlux, so that I can release the MVP quickly until I can learn WebFlux properly."

• Refactor service calls to RestTemplate over WebClient

Acceptance Criteria 🎉

• Ensure that all code conforms to our coding standards
• Written new unit / integration tests (or updated existing ones) for changes if necessary
• Verified that all unit / integration tests are passing
• Written doc blocks, inline documentation and updated READMEs on all new changes if necessary
• Both Travis CI and SonarCloud are passing

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