Update Import external scripts in Dynamic Text

[mikhail-vl]

Necessary changes:

• Update screenshots
• Remove mentioning of external scripts editor (since es modules approach is recommended, thie previous one is not supported)
• Disabling sanitizing is not required anymore because we can't prohibit a using import function
• Describe how to use a not esm npm package. Convert with https://esm.sh/#docs and use it. Eg. https://www.npmjs.com/package/flatpickr - esm is not supported and unable to use with import(). But can be converted and used https://esm.sh/flatpickr (a working example with flatpickr - DT with Grafana 11 fails for Date-Picker flatpickr volkovlabs-dynamictext-panel#309 (comment))
• Use this in afterRender code to keep data for next updates. Eg. destroy chart before creating a new one. It's show in chart.js example

Following #684