Switch activity refactor experiment flag to opt-out

We're flipping the functionality of the workspace activity experiment from opt-in to opt-out. This way customers default to the improved stability with the option to revert.

Upon the next release, if any of the CLI, VSCode Extension, JetBrains extension, or agent are behind the required version for compatibility with the activity refactor, user activity may be dropped or misreported from the outdated source. This impacts template insights and workspace scheduling features. The required versions for each of these have already been released:

Product | Required Version | Repo
------- | ---------------- | ----
Coder CLI | >=[`v2.13.0`](https://github.com/coder/coder/releases/tag/v2.13.0) | coder/coder
Workspace Agents | >=[`v2.13.0`](https://github.com/coder/coder/releases/tag/v2.13.0) | coder/coder
Jetbrains ext. | >=[`v2.12.0`](https://github.com/coder/jetbrains-coder/releases/tag/v2.12.0) | coder/jetbrains-coder
~VSCode ext.~ | Works as long as CLI is up-to-date | ~coder/vscode-coder~

We'll call out this risk in the release changelog when flipped.