Convert sidebar_header component to typescript

[ayusht2810]

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

[Willy-Wakam]

Can I work on this?

[ayusht2810]

Thanks, @Willy-Wakam!

[mickmister]

Hi @Willy-Wakam, I noticed you claimed a few tickets at once. Just touching base and making sure you still want to work on these. Also note that we are in the process of fixing the projects to make the experience better. Thanks for your contributions!

[mickmister]

@Willy-Wakam Also note that we typically want to have only a small amount of tickets claimed at once by one person, in order to have more available to work on. But as I mentioned, these particular tickets can be made easier to work on first. The core parts of the project and CI need to be fixed and verified.