This PR was squashed before being merged into the 7.3 branch.

Discussion
----------

[Cache] Add `\Relay\Cluster` support

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Issues        | n/a
| License       | MIT

This PR allows usage of the `\Relay\Cluster` class in `RedisAdapter` when [relay](https://relay.so/) extension is installed in version >= 0.10.0.

## Example usage

### Creating a connection with auth

Note that `\Relay\Cluster` will only be used if `relay` extension is loaded

```php
use Symfony\Component\Cache\Adapter\RedisAdapter;

$relayCluster = RedisAdapter::createConnection(
    'redis:?host[valkey-cluster:6372]&host[valkey-cluster:6373]&host[valkey-cluster:6374]&auth=my-password&redis_cluster=1'
);

$cacheUsingRelayCluster = new RedisAdapter($relayCluster);
```

### Creating tls connection with self-signed certificate for testing in local environment

```php
use Symfony\Component\Cache\Adapter\RedisAdapter;

$relayCluster = RedisAdapter::createConnection(
    'rediss:?host[valkey-cluster:6372]&host[valkey-cluster:6373]&host[valkey-cluster:6374]&redis_cluster=1&relay_cluster_context[stream][verify_peer]=false&relay_cluster_context[stream][verify_peer_name]=false&relay_cluster_context[stream][allow_self_signed]=true&relay_cluster_context[stream][local_cert]=/valkey.crt&relay_cluster_context[stream][local_pk]=/valkey.key&relay_cluster_context[stream][cafile]=/valkey.crt&relay_cluster_context[max-retries]=5&relay_cluster_context[client-tracking]=false'
);
```

### Alternatively if you already have an instance of `\Relay\Cluster` which you want to use:
```php
use Relay\Cluster;
use Symfony\Component\Cache\Adapter\RedisAdapter;

$relayCluster = new Cluster(
    'my-relay-cluster-client',
    [
        'valkey-cluster-untracked:6372',
        'valkey-cluster-untracked:6373',
        'valkey-cluster-untracked:6374',
    ],
);

$cacheUsingRelayCluster = new RedisAdapter($relayCluster);
```

With this PR, two connection options have been introduced:
 - ~~`relay_cluster` which is a boolean indicating whether the user wants to create a `\Relay\Cluster` connection~~ Removed in favor of using `redis_cluster` and the fact that `relay` extension is loaded to choose the `\Relay\Cluster` class
 - `command_timeout` which is consumed by `\Relay\Cluster` and defaults to `0`
 - `relay_cluster_context` which is consumed by `\Relay\Cluster` and allows user to configure options described in cachewerk/relay#161 (comment)

CC: `@tillkruss`

Commits
-------

f4a76e0 [Cache] Add `\Relay\Cluster` support

This PR was merged into the 7.3 branch.

Discussion
----------

[Cache] Code cleanup

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Follows #59857 /cc `@dorrogeray` (some changes for the upcoming doc)

Commits
-------

922f5ff [Cache] Code cleanup