feat: multi dev branches (#4023)

Closes this feature request:
[https://triggerdev.featurebase.app/p/isolated-dev-sessions-for-multiple-local-trigger-dev-instances](https://triggerdev.featurebase.app/p/isolated-dev-sessions-for-multiple-local-trigger-dev-instances)

### Feature notes:
- CLI `trigger dev` works as before
- `trigger dev --branch my-branch` to create a new branch and run
against it.
- `trigger dev archive --branch my-branch` to archive (or in webapp).
- New webapp page to manage and archive dev branches, currently feature
flagged.

### Implementation details:
- No changes to data model, no backfill. `isBranchableEnvironment`
column is ignored for dev branches, we use `parentEnvironmentId IS NULL`
instead.
- `x-trigger-branch` overloaded for preview and dev branches
- New `TRIGGER_DEV_BRANCH` env var available locally.
`TRIGGER_PREVIEW_BRANCH` overloaded for child runs.
- Lots of new glue code to sanitise the branch checks.

### Rollout
- Deploy webapp/API changes (all backwards compatible)
- Manual tests on some orgs
- Deploy docs, release CLI, flip feature flag for webapp feature

### NB
- `api.v1.projects.$projectRef.environments.ts` will return
`isBranchableEnvironment: true` for all dev environments.

### Prerequisites
- [x] Typecheck will not pass until we make a new release of
`@trigger.dev/platform` and bump it here

docs/docs.json

@@ -199,6 +199,7 @@
               "deploy-environment-variables",
               "github-actions",
               "deployment/preview-branches",
+              "deployment/dev-branches",
               "deployment/atomic-deployment",
               {
                 "group": "Deployment integrations",