document dump_to_file and load_from_file

docs/docs/administration/CLI_tasks/config.md

@@ -155,3 +155,42 @@ This forcibly removes all saved values in the database.
     ```sh
     mix pleroma.config [--force] reset
     ```
+
+## Dumping specific configuration values to JSON
+
+If you want to bulk-modify configuration values (for example, for MRF modifications),
+it may be easier to dump the values to JSON and then modify them in a text editor.
+
+=== "OTP"
+
+    ```sh
+    ./bin/pleroma_ctl config dump_to_file group key path
+    # For example, to dump the MRF simple configuration:
+    ./bin/pleroma_ctl config dump_to_file pleroma mrf_simple /tmp/mrf_simple.json
+    ```
+
+=== "From Source"
+
+    ```sh
+    mix pleroma.config dump_to_file group key path 
+    # For example, to dump the MRF simple configuration:
+    mix pleroma.config dump_to_file pleroma mrf_simple /tmp/mrf_simple.json
+    ```
+
+## Loading specific configuration values from JSON
+
+=== "OTP"
+
+    ```sh
+    ./bin/pleroma_ctl config load_from_file path
+    # For example, to load the MRF simple configuration:
+    ./bin/pleroma_ctl config load_from_file /tmp/mrf_simple.json
+    ```
+
+=== "From Source"
+
+    ```sh
+    mix pleroma.config load_from_file path
+    # For example, to load the MRF simple configuration:
+    mix pleroma.config load_from_file /tmp/mrf_simple.json
+    ```

lib/mix/tasks/pleroma/config.ex

@@ -79,7 +79,7 @@ def run(["dump", group]) do
     end)
   end
 
-  def run(["dump_to_file", group, key]) do
+  def run(["dump_to_file", group, key, fname]) do
     check_configdb(fn ->
       start_pleroma()
 
@@ -95,7 +95,7 @@ def run(["dump_to_file", group, key]) do
       |> Jason.encode!()
       |> Jason.Formatter.pretty_print()
 
-      File.write("#{group}_#{key}.json", json)
+      File.write(fname, json)
       shell_info("Wrote #{group}_#{key}.json")
     end)
   end