common: allow configvars to be marked dynamic.

To test, we do min-capacity-sat which is simple.  We also update the
listconfigs man page which contained some obsolete information.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

doc/lightning-listconfigs.7.md

@@ -9,12 +9,27 @@ SYNOPSIS
 DESCRIPTION
 -----------
 
-*config* (optional) is a configuration option name, or "plugin" to show plugin options
+*config* (optional) is a configuration option name to restrict return.
 
-The **listconfigs** RPC command to list all configuration options, or with *config* only a selection.
+The **listconfigs** RPC command to list all configuration options, or with *config* only one.
 
 The returned values reflect the current configuration, including
-showing default values (`dev-` options are not shown).
+showing default values (`dev-` options are not shown unless specified as *config* explicitly).
+
+Note: as plugins can add options, not all configuration settings are
+listed here!  The format of each entry is as follows:
+
+- **source** (string): source of configuration setting (`file`:`linenum`)
+- **dynamic** (boolean, optional): true if this option is settable via setconfig
+- **plugin** (string, optional): set if this is from a plugin
+
+Depending on the option type, exactly one of the following is present:
+
+- **set** (boolean, optional): for simple flag options
+- **value\_str** (string, optional): for string options
+- **value\_msat** (msat, optional): for msat options
+- **value\_int** (integer, optional): for integer options
+- **value\_bool** (boolean, optional): for boolean options
 
 EXAMPLE JSON REQUEST
 --------------------
@@ -177,6 +192,7 @@ On success, an object is returned, containing:
   - **min-capacity-sat** (object, optional):
     - **value\_int** (u64): field from config or cmdline, or default
     - **source** (string): source of configuration setting
+    - **dynamic** (boolean, optional): Can this be set by setconfig() (always *true*)
   - **addr** (object, optional):
     - **values\_str** (array of strings):
       - field from config or cmdline
@@ -447,4 +463,4 @@ RESOURCES
 
 Main web site: <https://github.com/ElementsProject/lightning>
 
-[comment]: # ( SHA256STAMP:2b3588b395919162c122cd386f0f4b320d906d0190e706bfa1b68db4126e7ee2)
+[comment]: # ( SHA256STAMP:0440e4634e4a28681323f891307c7bb61143aacad4824f952f24f027a7543835)

doc/schemas/listconfigs.schema.json

@@ -834,6 +834,13 @@
             "source": {
               "type": "string",
               "description": "source of configuration setting"
+            },
+            "dynamic": {
+              "type": "boolean",
+              "enum": [
+                true
+              ],
+              "description": "Can this be set by setconfig()"
             }
           }
         },