Update Dockerfile: bump alpine (#20897)

* Update Dockerfile: bump alpine

* Create 20897

* Rename 20897 to 20897.txt

.changelog/20897.txt

@@ -0,0 +1,3 @@
+```release-note:security
+ Bump Dockerfile base image to `alpine:3.19`. 
+ ```

Dockerfile

@@ -112,7 +112,7 @@ CMD ["agent", "-dev", "-client", "0.0.0.0"]
 
 # Production docker image that uses CI built binaries.
 # Remember, this image cannot be built locally.
-FROM docker.mirror.hashicorp.services/alpine:3.18 as default
+FROM docker.mirror.hashicorp.services/alpine:3.19 as default
 
 ARG PRODUCT_VERSION
 ARG BIN_NAME