chore: switch to using submodules for docs

Signed-off-by: Vibhu Prashar <vibhu.sharma2929@gmail.com>

Author: vprashar2929

.gitmodules

@@ -0,0 +1,8 @@
+[submodule "docs/submodules/kepler"]
+	path = docs/submodules/kepler
+	url = https://github.com/sustainable-computing-io/kepler.git
+	branch = main
+[submodule "docs/submodules/kepler-operator"]
+	path = docs/submodules/kepler-operator
+	url = https://github.com/sustainable-computing-io/kepler-operator.git
+	branch = v1alpha1