message: Enhance linked services for MySQL, PostgreSQL, Teradata and DB2
diff: "MySqlLinkedServiceTypeProperties": {
  "description": "MySQL linked service properties.",
  "properties": {
  - "server": {
  - "type": "object",
  - "description": "Server name for connection. Type: string (or Expression with resultType string)."
  - },
  - "database": {
  - "type": "object",
  - "description": "Database name for connection. Type: string (or Expression with resultType string)."
  - },
  - "schema": {
  - "type": "object",
  - "description": "Schema name for connection. Type: string (or Expression with resultType string)."
  - },
  - "username": {
  - "type": "object",
  - "description": "Username for authentication. Type: string (or Expression with resultType string)."
  - },
  - "password": {
  - "description": "Password for authentication.",
  + "connectionString": {
  + "description": "The connection string.",
  "$ref": "../datafactory.json#/definitions/SecretBase"
  },
  "encryptedCredential": {
  }
  },
  "required": [
  - "server",
  - "database"
  + "connectionString"
  ]
  },
  "PostgreSqlLinkedService": {
  "PostgreSqlLinkedServiceTypeProperties": {
  "description": "PostgreSQL linked service properties.",
  "properties": {
  - "server": {
  - "type": "object",
  - "description": "Server name for connection. Type: string (or Expression with resultType string)."
  - },
  - "database": {
  - "type": "object",
  - "description": "Database name for connection. Type: string (or Expression with resultType string)."
  - },
  - "schema": {
  - "type": "object",
  - "description": "Schema name for connection. Type: string (or Expression with resultType string)."
  - },
  - "username": {
  - "type": "object",
  - "description": "Username for authentication. Type: string (or Expression with resultType string)."
  - },
  - "password": {
  - "description": "Password for authentication.",
  + "connectionString": {
  + "description": "The connection string.",
  "$ref": "../datafactory.json#/definitions/SecretBase"
  },
  "encryptedCredential": {
  }
  },
  "required": [
  - "server",
  - "database"
  + "connectionString"
  ]
  },
  "SybaseLinkedService": {
  "type": "object",
  "description": "Database name for connection. Type: string (or Expression with resultType string)."
  },
  - "schema": {
  - "type": "object",
  - "description": "Schema name for connection. Type: string (or Expression with resultType string)."
  - },
  "authenticationType": {
  "description": "AuthenticationType to be used for connection.",
  "type": "string",
  "type": "object",
  "description": "Server name for connection. Type: string (or Expression with resultType string)."
  },
  - "schema": {
  - "type": "object",
  - "description": "Schema name for connection. Type: string (or Expression with resultType string)."
  - },
  "authenticationType": {
  "description": "AuthenticationType to be used for connection.",
  "type": "string",
  