Setting Amazon Lex session attributes

AgentX provides support for an item to set Amazon Lex session attributes. There are two ways to achieve this.

Use the handlebars helper setSessionAttr in an answer. For example, the following code will set an attribute called attributeName to the value attributeValue.
```
{{setSessionAttr 'attributeName' 'attributeValue'}}
```
Use the dedicated session attribute field to set a name/value pair.

The attribute name can be a simple name like myAttribute or a complex name like myAttribute.subAttribute. You can also use the dot notation to set an attribute several levels deep.

NOTE: Avoid using appContext or qnabotcontext as attribute names. Setting these may have adverse effects on the system.

Canonical Session Attributes

Attribute Name	Set By	Meaning
`x-paragon-agentx:voice:next-action`	User	Next action to take. See table below for possible values
`x-paragon-agentx:voice:skip-next-prompt`	User	If `true`, do not prompt for the next question
`x-paragon-agentx:voice:pstn-target`	User	If the next-action is `PSTN-TRANSFER`, must contain an E.164 phone number
`x-paragon-agentx:voice:sip-target`	User	If the next-action is `SIP-TRANSFER`, must contain a URL
`x-paragon-agentx:connect:queue-target`	User	If the next-action is `QUEUE-TRANSFER`, must contain the ID of an Amazon Connect queue
`x-paragon-agentx:customer:src-number`	AgentX	The source number of the phone call
`x-paragon-agentx:customer:dst-number`	AgentX	The destination number of the phone call
`x-paragon-agentx:smt:message`	User	Sets the message to be texted. If not set the last chatbot response in the chat history is sent.

Value	Behavior
`TERMINATE`	Hangup or end a chat contact
`PSTN-TRANSFER`	Transfer to a phone number
`SIP-TRANSFER`	Transfer to a SIP endpoint
`QUEUE-TRANSFER`	Transfer to an Amazon Connect queue