fix(build): use buildx --load and non-registry image tag (#6419)

Co-authored-by: Gergely Bräutigam <gergely.brautigam@sap.com>
Signed-off-by: Alexander Chernov <alexander@chernov.it>

hack/api-docs/Makefile

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 DOCKER ?= docker
-MKDOCS_IMAGE ?= github.com/external-secrets-mkdocs:latest
+MKDOCS_IMAGE ?= eso-mkdocs:latest
 MKDOCS ?= mkdocs
 MIKE ?= mike
 DOCS_VERSION ?= main
@@ -47,7 +47,7 @@ all: build
 
 .PHONY: image
 image:
-	$(DOCKER) build -t $(MKDOCS_IMAGE) -f Dockerfile .
+	$(DOCKER) buildx build --load -t $(MKDOCS_IMAGE) -f Dockerfile .
 
 VERSION_TO_UPDATE ?= $(shell echo $(MAJOR_VERSION).$(MINOR_VERSION).x)