chore(deps): update stackitcloud/stackit requirement from ~> 0.99.0 to ~> 0.104.0

Updates the requirements on [stackitcloud/stackit](https://github.com/stackitcloud/terraform-provider-stackit) to permit the latest version.
- [Release notes](https://github.com/stackitcloud/terraform-provider-stackit/releases)
- [Changelog](https://github.com/stackitcloud/terraform-provider-stackit/blob/main/RELEASE.md)
- [Commits](stackitcloud/terraform-provider-stackit@v0.99.0...v0.104.0)

---
updated-dependencies:
- dependency-name: stackitcloud/stackit
  dependency-version: 0.104.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

src/modules/namespace-service-demo/main.tf

@@ -2,7 +2,7 @@ terraform {
   required_providers {
     stackit = {
       source  = "stackitcloud/stackit"
-      version = "~> 0.99.0"
+      version = "~> 0.104.0"
     }
     grafana = {
       source  = "grafana/grafana"