Add configuration files and misc. files like package-lock.json to .gitignore about bilbilet

[can-aslan]

package-lock.json did exist in the repository at some point but yes, it does not exist in the repository anymore. I gave it as an example file which could be removed. For me, it looks like no unnecessary config files exist in the frontend. We have some in the backend though.

[selimcanglr]

I don't think we have package-lock.json files on the frontend side. We have package.json which is necessary for installing the npm packages and yarn.lock which is again necessary for the integrity of the installed packages. Other than that, prettier config files and tsconfig files are neccesary so that we all share the same convention with regards to formatting and all.

[selimcanglr]

I am not sure which files are unnecessary in the backend folder but maybe @tolgaozgun knows better.

[can-aslan]

This does not seem to be an issue anymore.