Added esbuild task for building minified version

[Hecatron]

Hi,
I was looking to see if there was a minified version of jssip that could be downloaded
but it looks as if the scripts for generating one were removed from the source.

I've added one to npm-scripts.js / package.json that runs esbuild
This is quite a bit faster than the original Browserify
I've also added /dist/ to .gitignore since normally you wouldn't want to include minified code into the github repo directly

What should be possible after this, is to add a line to the release function to run the build
then you could add an entry to package.json to also copy /dist/jssip.min.js into the final package published to npmjs
This is the way I think most other packages tend to do it

[ibc]

There isn't any good reason in 2026 to generate minified JS libraries. Those who use JsSIP are supposed to integrate it into a larger application built with React, Vue, webpack, etc, rather than integrating JsSIP into their website as if it was year 2005.

[Hecatron]

There are situations where a minified file is useful, typically in cases outside of js frameworks
Or if you want to download via a cdn

• Use of a non js framwework such as blazor - [JSImport]
  https://learn.microsoft.com/en-us/aspnet/core/blazor/javascript-interoperability/?view=aspnetcore-10.0
• Use in rust / web assembly
  https://book.leptos.dev/web_sys.html