query args from GET requests are put into our logs, and we should avoid
personal data (eg phone numbers) in them. Remove this old GET now that
it's not used by the admin app anymore
also, it should default to last 7 days, not last 6 days. also change
count_inbound_sms to have the days passed in, so that it's more
explicit at the endpoint that we only return 7 days regardless of your
service's data retention
rather than using the `normalise_phone_number` function, use the
`validate_and_format_phone_number` function - this will also convert
all numbers to international format, which means we won't need to
worry about whether the user enters internaional or UK phone numbers
when searching
two endpoints:
* get all inbound sms for a service (you can limit to the X most
recent, or filter by user's phone number [which will be normalised])
* get a summary of inbound sms for a service - returns the count of
inbound sms in the database, and the date that the most recent was
sent
