Documentation for Salesforce DLS (#2056)

Co-authored-by: Liam Thompson <32779855+leemthompo@users.noreply.github.com>

Author: moxarth-rathod

docs/document-level-security/SALESFORCE.md

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+### Setting up the Salesforce connector
+
+See the [Developer guide](../../docs/DEVELOPING.md) for setting up connectors.
+
+## Document level security
+
+Document level security (DLS) enables you to restrict access to documents based on a user'­s permissions. This feature is available by default for the Salesforce connector.
+Salesforce connector DLS supports for both standard & custom objects.
+
+Refer to [document level security](https://www.elastic.co/guide/en/enterprise-search/master/dls.html) for more information.
+
+Salesforce allows users to set permissions in different ways i.e. via Profiles, Permission sets and Permission set Groups.
+
+For guidance, refer to these [video tutorials](https://howtovideos.hubs.vidyard.com/watch/B1bQnMFg2VyZq7V6zXQjPg#:~:text=This%20is%20a%20must%20watch,records%20in%20your%20Salesforce%20organization) about setting Salesforce permissions.
+
+To ingest any standard or custom objects, users must ensure that at least `Read` permission is granted to that object. This can be granted using any of the following methods for setting permissions.
+
+### Set Permissions using Profiles
+
+Refer to the [official documentation](https://help.salesforce.com/s/articleView?id=sf.admin_userprofiles.htm&type=5) for setting permissions via Profiles.
+
+### Set Permissions using Permissions Set
+
+Refer to the [official documentation](https://help.salesforce.com/s/articleView?id=sf.perm_sets_overview.htm&language=en_US&type=5) for setting permissions via Permissions Sets.
+
+### Set Permissions using Permissions Set group
+
+Refer to the [official documentation](https://help.salesforce.com/s/articleView?id=sf.perm_set_groups.htm&type=5) for setting permissions via Permissions Set Groups.
+
+### Set Profiles, Permission Set and Permission Set Groups to the User
+
+1. Go to `Administration` under the `Users` section.
+2. Select `Users` and choose the user to set the permissions to. 
+3. Set the `Profile`, `Permission Set`or `Permission Set Groups` created in the earlier steps.
+
+**Note:** Refer to [DLS in Search Applications](https://www.elastic.co/guide/en/enterprise-search/master/dls-e2e-guide.html) to learn how to ingest data with DLS enabled, when building a search application.
+
+#### Additional Configuration
+
+##### `Enable document level security`
+
+Toggle to enable [document level security (DLS)](https://www.elastic.co/guide/en/enterprise-search/master/dls.html). When enabled:
+- Full syncs will fetch access control lists for each document and store them in the `_allow_access_control` field.
+- Access control syncs will fetch users' access control lists and store them in a separate index.