Change the default port 5500 to a random port if it's already taken.

[Almo7aya]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  <!-- Please search GitHub for a similar issue or PR before submitting -->
[x] Feature request
[ ] Documentation issue or request
[ ] Other: <!-- Please describe: -->

Current behavior

When I'm working with multiple workspaces and want to live-server them both the extension forces me to change the port manually and that is so Annoying.

Expected behavior

Just like other command-line tools like live-server, if the default port is taken it fallback to a random one, regularly it adds +1 to the default port and continues serving.

Environment

Browser:

- [x] Chrome (desktop) version XX
- [ ] Firefox version XX
- [ ] Safari (desktop) version XX
- [ ] IE version XX
- [ ] Edge version XX

For Tooling issues:

- Live Server: 5.5.1
- Platform:  Windows 10
- Visual Studio Code: 1.31.1

Others

I think the owner of this project is currently busy, so I'll do it by myself.