…ors (#577)

This PR adds support for a new boolean option `ignoreProxyCertificate`. If set to `true`, certificate errors will be ignored, which can be useful for HTTPS proxies with self-signed certificates.

Usage:

```
const server = new Server({
  prepareRequestFunction: () => ({
    upstreamProxyUrl: 'https://user:pass@myproxy:8080',
    ignoreUpstreamProxyCertificate: true  // Useful for self-signed cert
  })
}).listen();
```
Anonymize:
```
anonymizeProxy({
  url: 'https://user:pass@myproxy:8080',
  ignoreProxyCertificate: true,
}).then((anonymizedURL) => {
  console.log(`Anonymized URL: ${anonymizedURL}`);
});
```
Create tunnel:
```
createTunnel(
  'https://user:pass@myproxy:8080',
  targetHost,
  { ignoreProxyCertificate: true }
).then((url) => {
  console.log('Tunnel endpoint:', url);
});
```