[GENERAL] Showcase module of a middleware or task using TypeScript

[tobiasqueck]

Is your feature request related to a problem? Please describe.
We as the maintainer of the in SAP Fiori tools and the Open UX tools (https://github.com/SAP/open-ux-tools) develop multiple custom tasks and middlewares. Our development language of choice is typescript, however, there are no types available for the API that is to be implemented by custom tasks and middlewares.

Describe the solution you'd like
Obviously, the right solution is to get the types provided by the ui5-tooling module (feature requested at SAP/ui5-tooling#651), however, it will take some time until that happens. In the meantime, we could provide a ui5-tooling-types module here, maintained by the community, so that we all can start building our tasks and middlewares with typescript. We could use https://github.com/SAP/open-ux-tools/blob/feat/687/deploy/packages/deploy-tooling/src/ui5/ui5.d.ts as a starting point.

Describe alternatives you've considered
Well, everyone, defines there own types locally.

Additional context
Since this is a showcase repository, we should also take one of the existing modules and convert it to typescript to show how it works.

[petermuessig]

Related to SAP/ui5-tooling#651 - waiting until this precondition is fulfilled!