feat(sessions): add support for remote redis session store (#3345)

Description
====================
zot currently stores session cookies in memory or in a local directory.
For cases where the session cookies should be independent of the
instance where they were created such as multiple instances of zot, or a
fully stateless zot instance, there is a need to support a remote
session storage.
This change adds support for using Redis and Redis-compatible services as a
remote session driver as well as introduces a new configuration option
for it.

What has changed
=======================
- New config added under Auth config to specify configuration for
  the session driver.
- Examples README updated with details of the new Auth config.
- The config supports only 2 drivers in this change - local and redis
- Using the local driver is backwards compatible and behaves the same
  way that zot currently works for local session storage.
- Omitting this config does not result in an error. In this case, zot
  behaves as it normally does for local session storage.
- When configured, zot can use redis for persisting cookie
  information for zot UI.
- The cookie in the store is deleted on logout or after the max
  expiry time for the cookie.
- Configuration for the redis session driver accepts the same configuration
  values as that of the remote meta cache.
- A separate connection is established for the session driver. An
  existing connection for meta cache will not be re-used for the
  session driver.
- A key prefix is configurable for the redis session driver. The value will be
  converted into a string for use. If no value is provided, a default
  prefix of "zotsession" will be used.
- Redis sessions does not support hash key or encryption in this change.
- New BATS test added to verify zot behavior with Redis session store.
- Github workflow updated to install valkey-tools dependency for BATS.

Signed-off-by: Vishwas Rajashekar <dev@vrajashkr.com>

pkg/api/config/config.go

@@ -75,8 +75,9 @@ type AuthConfig struct {
 	OpenID            *OpenIDConfig
 	APIKey            bool
 	SessionKeysFile   string
-	SessionHashKey    []byte `json:"-"`
-	SessionEncryptKey []byte `json:"-"`
+	SessionHashKey    []byte         `json:"-"`
+	SessionEncryptKey []byte         `json:"-"`
+	SessionDriver     map[string]any `mapstructure:",omitempty"`
 }
 
 type BearerConfig struct {