Chat: update chat history export button (#5535)

This fixes an issue where clicking on the "Export" chat history button
in Eclipse would open the chat history as json in the current webview,
instead of showing up as a download dialogue.

- Open the blob link in a new window instead of current window
- Add timestamp to the downloaded file name to make it unique
- Update Content Security Policy to allow more connections for the
webview

## Test plan

<!-- Required. See
https://docs-legacy.sourcegraph.com/dev/background-information/testing_principles.
-->

Run this branch in Eclipse to confirm the Chat History export button
works. Here is a demo when running this branch from the latest eclipse
main branch:


https://github.com/user-attachments/assets/4ef85c4d-0cb5-4130-9d57-c4e5c78183db

## Changelog

<!-- OPTIONAL; info at
https://www.notion.so/sourcegraph/Writing-a-changelog-entry-dd997f411d524caabf0d8d38a24a878c
-->

vscode/webviews/CodyPanel.tsx

@@ -56,9 +56,11 @@ export const CodyPanel: FunctionComponent<
         const json = JSON.stringify(userHistory, null, 2)
         const blob = new Blob([json], { type: 'application/json' })
         const url = URL.createObjectURL(blob)
-        const a = document.createElement('a')
+        const timestamp = new Date().toISOString().replace(/[:.]/g, '-').slice(0, -5) // Format: YYYY-MM-DDTHH-mm
+        const a = document.createElement('a') // a temporary anchor element
         a.href = url
-        a.download = 'cody-chat-history.json'
+        a.download = `cody-chat-history-${timestamp}.json`
+        a.target = '_blank'
         a.click()
     }, [userHistory])
 

vscode/webviews/index.html

@@ -9,7 +9,7 @@
         <!-- This content security policy also implicitly disables inline scripts and styles. -->
         <meta
             http-equiv="Content-Security-Policy"
-            content="default-src 'none'; img-src 'self' https: data:; script-src 'self'; style-src 'self'; font-src data: 'self';"
+            content="default-src 'none'; img-src 'self' https: data:; script-src 'self'; style-src 'self'; font-src data: 'self'; connect-src 'self'; object-src 'self'; frame-src 'self'; media-src blob:;"
         />
         <!-- DO NOT REMOVE: THIS FILE IS THE ENTRY FILE FOR CODY WEBVIEW -->
         <!-- END CSP -->