Is there a way to have the data in the 2.0 chart node survive restarts?

### Description

The V1 chart has a tested and working subflow that saves the data and reloads the data
after a restart. This is pretty vital functionality and needed for V2 charts.
Can someone have look at this when there is time please?

I tested the old working subflow with the V 2 chart and as expected it does not work.
It would be great if this subflow could be updated to work with 2.0.
or of course any other way to have the data survive reboots if possible?
This is the subflow that worked with V1 hooked up to a V2 chart for tests:

```
[
{
"id": "3b6a1337b69e1574",
"type": "subflow",
"name": "vvb d2",
"info": "",
"category": "",
"in": [
{
"x": 50,
"y": 30,
"wires": [
{
"id": "0803c4cc5eb6de01"
}
]
}
],
"out": [
{
"x": 820,
"y": 160,
"wires": [
{
"id": "1d445f73ea677ec2",
"port": 0
},
{
"id": "de6cdd9bd32b3eb1",
"port": 0
}
]
}
],
"env": [],
"meta": {},
"color": "#DDAA99"
},
{
"id": "1d445f73ea677ec2",
"type": "file",
"z": "3b6a1337b69e1574",
"name": "",
"filename": "",
"appendNewline": true,
"createDir": true,
"overwriteFile": "true",
"x": 660,
"y": 140,
"wires": [
[]
]
},
{
"id": "006debb5e922bb46",
"type": "file in",
"z": "3b6a1337b69e1574",
"name": "",
"filename": "",
"format": "utf8",
"sendError": true,
"x": 500,
"y": 180,
"wires": [
[
"de6cdd9bd32b3eb1"
]
]
},
{
"id": "e37d519cbbd162d3",
"type": "json",
"z": "3b6a1337b69e1574",
"name": "",
"x": 500,
"y": 140,
"wires": [
[
"1d445f73ea677ec2"
]
]
},
{
"id": "de6cdd9bd32b3eb1",
"type": "json",
"z": "3b6a1337b69e1574",
"name": "",
"x": 660,
"y": 180,
"wires": [
[]
]
},
{
"id": "0803c4cc5eb6de01",
"type": "function",
"z": "3b6a1337b69e1574",
"name": "LoadSave",
"func": "var strSafe=msg.topic;\nif(strSafe)\n{\n strSafe=strSafe.replace(/[^a-z0-9]/gi, '_').toLowerCase();\n var loaded=context.get(strSafe)||0;\n msg.filename =\"/home/hb19/.node-red/flowsave/vvbd2/\"+strSafe+\".dat\";\n //node.warn(loaded);\n if(0===loaded)\n {\n //load chart!! \n msg.payload=\"load\";\n context.set(strSafe,1);\n \n //node.warn(\"Loading \" +strSafe);\n }\n else\n {\n //node.warn(\"Writing \" +strSafe);\n }\n return msg; \n}\nreturn null;\n\n",
"outputs": 1,
"timeout": "",
"noerr": 0,
"initialize": "",
"finalize": "",
"libs": [],
"x": 200,
"y": 160,
"wires": [
[
"abd9aa795d47fbc6"
]
]
},
{
"id": "abd9aa795d47fbc6",
"type": "switch",
"z": "3b6a1337b69e1574",
"name": "Load data",
"property": "payload",
"propertyType": "msg",
"rules": [
{
"t": "neq",
"v": "load",
"vt": "str"
},
{
"t": "eq",
"v": "load",
"vt": "str"
}
],
"checkall": "false",
"repair": false,
"outputs": 2,
"x": 350,
"y": 160,
"wires": [
[
"e37d519cbbd162d3"
],
[
"006debb5e922bb46"
]
]
},
{
"id": "3dc8c1a1d345ef1d",
"type": "ui-chart",
"z": "98b31619.daed3",
"g": "120d335300e6531b",
"group": "f83d15d3a238accd",
"name": "vvb chart week",
"label": "",
"order": 4,
"chartType": "line",
"category": "topic",
"categoryType": "msg",
"xAxisLabel": "",
"xAxisProperty": "",
"xAxisPropertyType": "property",
"xAxisType": "time",
"xAxisFormat": "",
"xAxisFormatType": "auto",
"yAxisLabel": "",
"yAxisProperty": "",
"ymin": "15",
"ymax": "65",
"action": "append",
"stackSeries": false,
"pointShape": "line",
"pointRadius": "2",
"showLegend": false,
"removeOlder": 1,
"removeOlderUnit": "604800",
"removeOlderPoints": "",
"colors": [
"#ff9300",
"#00fdff",
"#ff7f0e",
"#2ca02c",
"#a347e1",
"#d62728",
"#ff9896",
"#9467bd",
"#c5b0d5"
],
"textColor": [
"#ffffff"
],
"textColorDefault": false,
"gridColor": [
"#7a7a7a"
],
"gridColorDefault": false,
"width": "30",
"height": "10",
"className": "",
"x": 4420,
"y": 540,
"wires": [
[
"2e85ceab3abb96f6"
]
]
},
{
"id": "2e85ceab3abb96f6",
"type": "subflow:3b6a1337b69e1574",
"z": "98b31619.daed3",
"g": "120d335300e6531b",
"name": "",
"x": 4430,
"y": 600,
"wires": [
[
"3dc8c1a1d345ef1d"
]
]
},
{
"id": "f83d15d3a238accd",
"type": "ui-group",
"name": "vvb",
"page": "40ab10feb1ddf2bb",
"width": "30",
"height": "20",
"order": 1,
"showTitle": false,
"className": "",
"visible": "true",
"disabled": "false"
},
{
"id": "40ab10feb1ddf2bb",
"type": "ui-page",
"name": "vvb",
"ui": "cd62f850b848415c",
"path": "/vvb",
"icon": "home",
"layout": "grid",
"theme": "404b2b83a6155d6c",
"breakpoints": [
{
"name": "Default",
"px": "0",
"cols": "30"
},
{
"name": "Tablet",
"px": "1080",
"cols": "30"
},
{
"name": "Small Desktop",
"px": "1080",
"cols": "30"
},
{
"name": "Desktop",
"px": "1080",
"cols": "30"
}
],
"order": 1,
"className": "",
"visible": true,
"disabled": false
},
{
"id": "cd62f850b848415c",
"type": "ui-base",
"name": "flax 24",
"path": "/dashboard",
"includeClientData": true,
"acceptsClientConfig": [
"ui-notification",
"ui-control"
],
"showPathInSidebar": false,
"showPageTitle": false,
"navigationStyle": "default",
"titleBarStyle": "default"
},
{
"id": "404b2b83a6155d6c",
"type": "ui-theme",
"name": "dark jtm",
"colors": {
"surface": "#000000",
"primary": "#0094ce",
"bgPage": "#000000",
"groupBg": "#000000",
"groupOutline": "#000000"
},
"sizes": {
"pagePadding": "12px",
"groupGap": "12px",
"groupBorderRadius": "4px",
"widgetGap": "12px",
"density": "comfortable"
}
}
]
```

### Have you provided an initial effort estimate for this issue?

I am no FlowFuse team member

Start with the supplied V1 LoadSave subflow and the ui-chart configuration, then compare how the V2 chart handles incoming and restored data across a restart. Done means a documented, tested approach reliably restores chart data after reboot without depending on the V1 chart implementation.

Written by the indexing model from the issue text.