feat: add upstash-redis driver

.gitignore

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 /test.*
 __*
 .vercel
+.env

docs/content/6.drivers/upstash.md

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+## Upstash Redis
+
+The `redis-upstash` driver is an [Upstash](https://upstash.com/) based HTTP only driver that can be used in environments where TCP isn't available.
+
+```ts
+import { createStorage } from "unstorage";
+import redisUpstashDriver from "unstorage/drivers/redis-upstash";
+
+const storage = createStorage({
+  driver: redisUpstashDriver({
+    base: "unstorage",
+    url: "https://your-upstash-db.com",
+    token: "your-token",
+  }),
+});
+```
+
+**Options:**
+
+- `url`: Url of your upstash redis database. This will default to the value of the `UPSTASH_REDIS_REST_URL` environment variable if not provided.
+- `token`: Authorization token. This will default to the value of the `UPSTASH_REDIS_REST_TOKEN` environment variable if not provided.
+- `base`: Optional prefix to use for all keys. Can be used for namespacing. Has to be used as hastag prefix for redis cluster mode.
+- `envPrefix`: Optional prefix for your environment variables. Defaults to `UPSTASH_REDIS_REST`.
+- `ttl`: Default TTL for all items in **seconds**.
+
+See [upstash driver docs](https://github.com/upstash/upstash-redis) for all available options.
+
+**Transaction options:**
+
+- `ttl`: Supported for `setItem(key, value, { ttl: number /* seconds */ })`