Added SNMP Table refresh (#8411)

* added guide to get started in GUI development

* added description for pages and httpdocs

* added timer for table refresh

* GUI develooper docs

---------

Co-authored-by: DGabri <gabriele.deri@gmail.com>
Co-authored-by: Matteo Biscosi <49585191+MatteoBiscosi@users.noreply.github.com>

doc/developers/README.GUI.quickstart.md

@@ -0,0 +1,32 @@
+## GUI utilization guide
+
+This guide is a quickstart to get up and running for GUI development
+
+1. Make sure to have node.js installed
+2. Run `npm install` to install all the dependencies
+3. Before making changes to any page make sure to run `npm run watch` so that changes are displayed after every file save
+4. After having made changes please build with the appropriate command.
+    - `npm run build:ntopng.js` to compile js only. If CSS changes have not been done
+    - `npm run build:ntopng.js` to compile css only. If JS changes have not been done
+    - `npm run build` to compile all the changes
+
+## Project structure
+
+The folder `http_src/` contains all the webpages scripts. 
+
+- `http_src/vue` contains single vue components that are imported in desired pages
+- `http_src/utilities` contains all utility functions 
+- `http_src/ntopng.js` contains all global imports that will be visible inside single components
+- `pages/` is found in `httpdocs/templates/pages/`
+- `httpdocs/` is the folder for GUI data, dist folder is present inside it
+- `template.render("pages/vue_page.template", { vue_page_name = "PageSNMPDevices", page_context = json_context })` some .lua pages render vue components. The name of the component is the value of `vue_page_name`, in this case the component is `PageSNMPDevices`. This is the name of the component importend in the script `http_src/vue/ntop_vue.js`. This is the import: `import { default as PageSNMPDevices } from "./page-snmp-devices.vue"` where PageSNMPDevices is the name of the vue component imported and displayed on the webpage and the component is found in the file page-snmp-devices.vue
+
+## Webpage structure
+
+Pages are rendered lua side, rendering .vue components inside of the pages that need them.
+
+- How to find .vue components that are used on a page?
+    1. take the path of the current webpage and the .lua file that renders it is found
+    2. prepend `scipts/` to the page path and the file is opened
+    3. `template.render("VUE-COMPONENT-PATH", { vue_page_name = "PAGE-NAME", page_context = json_context })` this function renders VUE-COMPONENT-PATH vue component
+- Each page has a `page=*` parameter where * is the name of the page. * is used to route each page and have conditional rendering lua side