Docs: Add plugins guide on error handling (#26518)

docs/sources/developers/plugins/error-handling.md

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+title = "Error handling"
+type = "docs"
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+
+# Error handling
+
+This guide explains how to handle errors in plugins.
+
+## Provide usable defaults
+
+Allow the user to learn your plugin in small steps. Provide a useful default configuration so that:
+
+- The user can get started right away.
+- You can avoid unnecessary error messages.
+
+For example, by selecting the first field of an expected type, the panel can display a visualization without any user configuration. If a user explicitly selects a field, then use that one. Otherwise, default to the first field of type `string`:
+
+```ts
+const numberField = frame.fields.find(field =>
+  options.numberFieldName ? field.name === options.numberFieldName : field.type === FieldType.number
+);
+```
+
+## Display error messages
+
+To display an error message to the user, `throw` an `Error` with the message you want to display:
+
+```ts
+throw new Error('An error occurred');
+```
+
+Grafana displays the error message in the top-left corner of the panel.
+
+{{< docs-imagebox img="/img/docs/panel_error.png" class="docs-image--no-shadow" max-width="850px" >}}
+
+Avoid displaying overly-technical error messages to the user. If you want to let technical users report an error, consider logging it instead.
+
+```ts
+try {
+  failingFunction();
+} catch (err) {
+  console.error(err);
+  throw new Error('Something went wrong');
+}
+```
+
+> **Note:** Grafana displays the exception message in the UI as written, so we recommend using grammatically correct sentences. For more information, refer to the [Documentation style guide](https://github.com/grafana/grafana/blob/master/contribute/style-guides/documentation-style-guide.md).
+
+Here are some examples of situations where you might want to display an error to the user.
+
+### Invalid query response
+
+Users have full freedom when they create data source queries for panels. If your panel plugin requires a specific format for the query response, then use the panel canvas to guide the user.
+
+```ts
+if (!numberField) {
+  throw new Error('Query result is missing a number field')
+}
+
+if (frame.length === 0) {
+  throw new Error('Query returned an empty result')
+}
+```