Give connectors a store that survives restarts, and a way to clear it

`ConnectorNode.store` keeps short strings per connector package in the
engine's database (`connector_state`, migration f8c3e5a91d27), so the nodes of
one package share them and `fluksio serve` needs nothing new: get, set and
delete, at most 64 kB a value and 256 keys a package. A superuser lists the
keys (never the values) and clears them through `/connectors/{node_type}/state`,
or under Stored state in a connector node's panel. Documented in the connector
contract.

frontend/src/client/schemas.gen.ts

@@ -565,6 +565,29 @@ export const ChatItemSchema = {
     title: 'ChatItem'
 } as const;
 
+export const ConnectorStatePublicSchema = {
+    properties: {
+        connector: {
+            type: 'string',
+            title: 'Connector'
+        },
+        data: {
+            items: {
+                '$ref': '#/components/schemas/StoredKey'
+            },
+            type: 'array',
+            title: 'Data'
+        },
+        count: {
+            type: 'integer',
+            title: 'Count'
+        }
+    },
+    type: 'object',
+    required: ['connector', 'data', 'count'],
+    title: 'ConnectorStatePublic'
+} as const;
+
 export const ControlNodeSchema = {
     properties: {
         id: {
@@ -3669,6 +3692,27 @@ export const ShareRequestSchema = {
     title: 'ShareRequest'
 } as const;
 
+export const StoredKeySchema = {
+    properties: {
+        key: {
+            type: 'string',
+            title: 'Key'
+        },
+        size: {
+            type: 'integer',
+            title: 'Size'
+        },
+        updated_at: {
+            type: 'string',
+            format: 'date-time',
+            title: 'Updated At'
+        }
+    },
+    type: 'object',
+    required: ['key', 'size', 'updated_at'],
+    title: 'StoredKey'
+} as const;
+
 export const SubscriptionSchema = {
     properties: {
         endpoint: {

frontend/src/client/types.gen.ts

@@ -142,6 +142,12 @@ export type ChatItem = {
     error?: (string | null);
 };
 
+export type ConnectorStatePublic = {
+    connector: string;
+    data: Array<StoredKey>;
+    count: number;
+};
+
 /**
  * A wren node the chat can talk to: where it sends and where it reads.
  */
@@ -1235,6 +1241,12 @@ export type ShareRequest = {
     lib_name: string;
 };
 
+export type StoredKey = {
+    key: string;
+    size: number;
+    updated_at: string;
+};
+
 /**
  * What a browser handed us. Opaque apart from the endpoint's host.
  */
@@ -1553,6 +1565,25 @@ export type CloudAddRemoteUserResponse = (UserPublic);
 
 export type CloudDisconnectResponse = (Message);
 
+export type ConnectorsReadConnectorStateData = {
+    nodeType: string;
+};
+
+export type ConnectorsReadConnectorStateResponse = (ConnectorStatePublic);
+
+export type ConnectorsClearConnectorStateData = {
+    nodeType: string;
+};
+
+export type ConnectorsClearConnectorStateResponse = (Message);
+
+export type ConnectorsDeleteConnectorStateData = {
+    key: string;
+    nodeType: string;
+};
+
+export type ConnectorsDeleteConnectorStateResponse = (Message);
+
 export type DashboardsReadDashboardsResponse = (DashboardsPublic);
 
 export type DashboardsReadDashboardData = {