Add MD design documents

Signed-off-by: Su <szhongna@amazon.com>

CHANGELOG.md

@@ -28,6 +28,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### 📝 Documentation
 
+* [MD] Add design documents of multiple data source feature [#2538](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2538)
 ### 🛠 Maintenance
 
 ### 🪛 Refactoring

src/plugins/data_source/README.md

@@ -5,50 +5,62 @@ An OpenSearch Dashboards plugin
 This plugin introduces support for multiple data sources into OpenSearch Dashboards and provides related functions to connect to OpenSearch data sources.
 
 ## Configuration
+
 Update the following configuration in the `opensearch_dashboards.yml` file to apply changes. Refer to the schema [here](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/data_source/config.ts) for supported configurations.
 
 1. The dataSource plugin is disabled by default; to enable it:
-`data_source.enabled: true`
+   `data_source.enabled: true`
 
 2. The audit trail is enabled by default for logging the access to data source; to disable it:
-`data_source.audit.enabled: false`
+   `data_source.audit.enabled: false`
 
- - Current auditor configuration:
-```
+- Current auditor configuration:
+
+```yml
 data_source.audit.appender.kind: 'file'
 data_source.audit.appender.layout.kind: 'pattern'
 data_source.audit.appender.path: '/tmp/opensearch-dashboards-data-source-audit.log'
 ```
 
 3. The default encryption-related configuration parameters are:
-```
+
+```yml
 data_source.encryption.wrappingKeyName: 'changeme'
 data_source.encryption.wrappingKeyNamespace: 'changeme'
-data_source.encryption.wrappingKey: [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
+data_source.encryption.wrappingKey:
+  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
 ```
+
 Note that if any of the encryption keyring configuration values change (wrappingKeyName/wrappingKeyNamespace/wrappingKey), none of the previously-encrypted credentials can be decrypted; therefore, credentials of previously created data sources must be updated to continue use.
 
 **What are the best practices for generating a secure wrapping key?**  
 WrappingKey is an array of 32 random numbers. Read [more](https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator) about best practices for generating a secure wrapping key.
 
 ## Public
+
 The public plugin is used to enable and disable the features related to multi data source available in other plugins. e.g. data_source_management, index_pattern_management
 
 - Add as a required dependency for whole plugin on/off switch
 - Add as opitional dependency for partial flow changes control
 
 ## Server
+
 The provided data source client is integrated with default search strategy in data plugin. When data source id presented in IOpenSearchSearchRequest, data source client will be used.
 
 ### Data Source Service
-The data source service will provide a data source client given a data source id and optional client configurations. 
+
+The data source service will provide a data source client given a data source id and optional client configurations.
 
 Currently supported client config is:
+
 - `data_source.clientPool.size`
 
 Data source service uses LRU cache to cache the root client to improve client pool usage.
+
 #### Example usage:
+
 In the RequestHandler, get an instance of the client using:
+
 ```ts
 client: OpenSearchClient = await context.dataSource.opensearch.getClient(dataSourceId);
 
@@ -57,21 +69,35 @@ apiCaller: LegacyAPICaller = context.dataSource.opensearch.legacy.getClient(data
 ```
 
 ### Data Source Client Wrapper
+
 The data source saved object client wrapper overrides the write related action for data source object in order to perform validation and encryption actions of the authentication information inside data source.
 
 ### Cryptography Client
+
 The research for choosing a suitable stack can be found in: [#1756](https://github.com/opensearch-project/OpenSearch-Dashboards/issues/1756)
+
 #### Example usage:
+
 ```ts
 //Encrypt
 const encryptedPassword = await this.cryptographyClient.encryptAndEncode(password);
 //Decrypt
 const decodedPassword = await this.cryptographyClient.decodeAndDecrypt(password);
 ```
+
 ---
 
 ## Development
 
 See the [OpenSearch Dashboards contributing
-guide](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/CONTRIBUTING.md) for instructions
-setting up your development environment.
+guide](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/CONTRIBUTING.md) for instructions setting up your development environment.
+
+### Design Documents
+
+- [High level design doc](./docs/high_level_design.md)
+- [User stories](./docs/user_stories.md)
+- [client management detail design](./docs/client_management_design.md)
+
+### Integrate with multiple data source feature
+
+TODO: [#2455](https://github.com/opensearch-project/OpenSearch-Dashboards/issues/2455)