environment: encapsulate the environment images are deployed to

This represents how our systems should integrate into their environment, typically using
some sort of agent, or commonly cloud-init.

In the future we could imagine this representing network configuration or any other kind
of configuration necessary to reach the environment as well.

For now EC2 and Azure is supported, and stub environments are
added to show the idea, but these are not implemented/used
yet.

internal/environment/environment.go

@@ -0,0 +1,25 @@
+package environment
+
+import "github.com/osbuild/osbuild-composer/internal/rpmmd"
+
+type Environment interface {
+	GetPackages() []string
+	GetRepos() []rpmmd.RepoConfig
+	GetServices() []string
+}
+
+type BaseEnvironment struct {
+	Repos []rpmmd.RepoConfig
+}
+
+func (p BaseEnvironment) GetPackages() []string {
+	return []string{}
+}
+
+func (p BaseEnvironment) GetRepos() []rpmmd.RepoConfig {
+	return p.Repos
+}
+
+func (p BaseEnvironment) GetServices() []string {
+	return []string{}
+}