Workspace Activity Experiment -> GA

After the initial completion of the workspace activity refactor https://github.com/coder/coder/issues/13279 in an experimental mode we want to continue to track any further improvements we've identified along the way. We also want to note any tasks that should be complete before graduating the feature to GA.

## Discussion
- [x] Should extending a workspace deadline update `last_used_at`? Should deadline extension be moved into `workspacestats.Reporter`?
- After discussing, we do not think that extending the workspace's deadline counts as "usage" and we will not be bumping `last_used_at`. It should (and current does) bump the `deadline`. If we need to bump `last_used_at` we always can, but it doesn't seem needed currently.
- [x] Should `coder port-forward` be included in template insights as it's own stat / app?
- Not right now. If product brings this up as a use case customers value we can circle back, but it would require more work on template insights than we want to do right now.
- [ ] Should session tracking stay in `agent_stats` or should we move this somewhere else? Would we rather they be `workspace_app_stats` long term?
- Long term we want to move this data out of `agent_stats` and into `workspace_app_stats` so that session like Jebrains are counted the same way other workspace apps are.
- Because the rolled up data is written to a new table, we do not need to backfill any data, we just need a new rollup query to run on experiment enabled.
- Because we would detect "vscode" as an app slug, this would conflict with any existing apps named "vscode". We should just combine them indiscriminately and do not try to block those names or reserve any app names.
- Removes hardcoded apps from the returned queries, we would search for those slugs when `convertTemplateInsightsApps` is called and use the matching `Seconds`.
- Need CLI to capture SessionID and continue to use it when reporting. CLI needs to report `started_at` with beginning of loop time, `ended_at` at `time.Now()` and sent every minute to ensure `last_used_at` is still updated. `insertWorkspaceAppStats` will handle session id conflict and update in DB.
- [x] Can / Should the methods on `workspacestats.Reporter` be combined for more robust activity reporting?
- No need currently.

## Preparation for GA release
- [ ] Remove SetEnv requests from Jetbrains extension ssh-config
- [ ] Remove SetEnv requests from vscode extension ssh-config
- [ ] Remove session tracking from agent ssh server
- [ ] Remove session tracking from `coderd` agent endpoints
- [ ] Remove `workspace-usage` experiment