alerting.matrix should allow client configuration including proxy-url

Describe the feature request

alerting.mattermost allows a proxy-url to be configured with alerting.mattermost.client.proxy-url

alerting:
  mattermost:
    webhook-url: http://mymattermost.example.com
    client:
      proxy-url: "http://myproxy:3128"

client.* parameters are ignored for matrix

I'm not fluent in Go but the

ClientConfig *client.Config `yaml:"client,omitempty"`

Is missing in alerting/provider/matrix/matrix.go https://github.com/TwiN/gatus/blob/7f3873d0b455a0d2bf7880eeee1dd0ea7391b2ab/alerting/provider/matrix/matrix.go#L27 ?

Why do you personally want this feature to be implemented?

In my env the matrix server is exclusively reachable through an internal proxy because outside of our network

How long have you been using this project?

9 months

Additional information

No response