feat: add collectionPrefix option (#88)

* add collection prefix

* change the opt name

* fix collection name in the index creations

* fix: prefix should be removed

* Update asyncPersistence.js

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update asyncPersistence.js

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* simplify the logic by removing the intermediate object

* add the usage of collectionPrefix into doc

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: MrZenW

README.md

@@ -35,6 +35,7 @@ It accepts a connections string `url` or you can pass your existing `db` object.
 - `db`: Existing MongoDB instance (if no `url` option is specified)
 - `dropExistingIndexes`: Flag used to drop any existing index previously created on collections (except default index `_id`)
 - `ttlAfterDisconnected`: Flag used to enable alternative behavior of the subscription ttl, the subscription will expire based on time since client last disconnected from the broker instead of time since the subscription was created.
+- `collectionPrefix`: Prefix to use for collection names (default: empty string)
 
 > When changing ttl durations or switching on/off **ttlAfterDisconnected** on an existing database, **dropExistingIndexes** needs to be set to true for ttl indexes to be updated.
 

asyncPersistence.js

@@ -88,12 +88,15 @@ class AsyncMongoPersistence {
       const databaseName = this.#opts.database || pathname
       this.#db = mongoDBclient.db(databaseName)
     }
+
+    const collectionPrefix = `${this.#opts.collectionPrefix || ''}`
+
     const db = this.#db
-    const subscriptions = db.collection('subscriptions')
-    const retained = db.collection('retained')
-    const will = db.collection('will')
-    const outgoing = db.collection('outgoing')
-    const incoming = db.collection('incoming')
+    const subscriptions = db.collection(`${collectionPrefix}subscriptions`)
+    const retained = db.collection(`${collectionPrefix}retained`)
+    const will = db.collection(`${collectionPrefix}will`)
+    const outgoing = db.collection(`${collectionPrefix}outgoing`)
+    const incoming = db.collection(`${collectionPrefix}incoming`)
     this.#cl = {
       subscriptions,
       retained,