Store bar location against user

[TomSeldon]

Currently a bar location has to be entered for each session. This would be better to change and store the user's choice so we do not have to ask them (or require they provide it) each time.

This involves:

• Add DynamoDB resource the serverless.yml
• On setting a bar location, store it (lots of docs available on this)
• Possibly (probably) add in basic state machine for obtaining bar location, and moving on to available questions

Possible flows:

First time user

> Alexa, ask Tiny Rebel to suggest a drink

[check if user has provided bar location before]
[=no]

>> Should I check Cardiff or Newport?

> Cardiff

[store bar location as Cardiff]

>> You might like.... (etc.)

Returning user with set bar location

> Alexa, ask Tiny Rebel to suggest a drink

[check if user has provided bar location before]
[=yes]

>> You might like.... (etc.)

Returning user, overriding bar location in request

> Alexa, ask Tiny Rebel to suggest a drink in Newport

[check if user has provided bar location before]
[=yes (Cardiff)]

>> You might like.... (etc.)

etc.

Alexa SDK supports state flows and per-user attributes as would be required to implement this. See SDK docs.