Convert sidebar_buttons component to typescript #430

We plan to migrate the gitlab plugin webapp over to TypeScript to facilitate better code quality. This Help Wanted issue is to modify the above mentioned file and associate test files (if the file exists).

Below is a checklist of items you should be doing to migrate:

• Rename the files to their associated TypeScript extensions (ie. js to ts, jsx to tsx).
• Add relevant types in the component(s) code.
• Update any components using those to the correct imports.
• Fix any errors generated by the TypeScript compiler. You can run rpm run check-types to display any errors.
  We are aiming to be as strict as possible for the time being, but if you run into any issues where the file cannot be successfully migrated without significant change in other libraries, or our tsconfig.json, please feel free to raise them as we are aiming to keep this process smooth and gradual, while enforcing as much as we can.

Some examples of already migrated files can be found here:

• [MM-47091] Migrate "components/integrations/abstract_outgoing_webhook.jsx" and tests to TypeScript mattermost#23977