community[minor]: fix redis store docstring and streamline initialization code (#22730)

Thank you for contributing to LangChain!

### Description

Fix the example in the docstring of redis store.
Change the initilization logic and remove redundant check, enhance error
message.

### Issue

The example in docstring of how to use redis store was wrong.

![image](https://github.com/langchain-ai/langchain/assets/37469330/78c5d9ce-ee66-45b3-8dfe-ea29f125e6e9)

### Dependencies
Nothing



- [ ] **Add tests and docs**: If you're adding a new integration, please
include
1. a test for the integration, preferably unit tests that do not rely on
network access,
2. an example notebook showing its use. It lives in
`docs/docs/integrations` directory.


- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

If no one reviews your PR within a few days, please @-mention one of
baskaryan, efriis, eyurtsev, ccurme, vbarda, hwchase17.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/community/langchain_community/storage/redis.py

@@ -18,7 +18,7 @@ class RedisStore(ByteStore):
             from langchain_community.utilities.redis import get_client
 
             client = get_client('redis://localhost:6379')
-            redis_store = RedisStore(client)
+            redis_store = RedisStore(client=client)
 
             # Set values for keys
             redis_store.mset([("key1", b"value1"), ("key2", b"value2")])
@@ -64,12 +64,15 @@ class RedisStore(ByteStore):
                 "pip install redis"
             ) from e
 
-        if client and redis_url or client and client_kwargs:
+        if client and (redis_url or client_kwargs):
             raise ValueError(
                 "Either a Redis client or a redis_url with optional client_kwargs "
                 "must be provided, but not both."
             )
 
+        if not client and not redis_url:
+            raise ValueError("Either a Redis client or a redis_url must be provided.")
+
         if client:
             if not isinstance(client, Redis):
                 raise TypeError(
@@ -86,7 +89,7 @@ class RedisStore(ByteStore):
         self.client = _client
 
         if not isinstance(ttl, int) and ttl is not None:
-            raise TypeError(f"Expected int or None, got {type(ttl)} instead.")
+            raise TypeError(f"Expected int or None, got {type(ttl)=} instead.")
 
         self.ttl = ttl
         self.namespace = namespace