## Problem
Safekeeper's OpenAPI spec is incorrect:
```
Semantic error at paths./v1/tenant/{tenant_id}/timeline/{timeline_id}.get.responses.404.content.application/json.schema.$ref
$refs must reference a valid location in the document
Jump to line 126
```
Checked on https://editor.swagger.io
## Summary of changes
- Add `NotFoundError`
- Add `description` and `license` fields to make Cloud OpenAPI spec
linter happy
Routes and their handlers were in a bit different order in 1) routes
list 2) their implementation 3) python client 4) openapi spec, making
addition of new ones intimidating. Make it the same everywhere, roughly
lexicographically but preserving some of existing logic.
No functional changes.
