Define Alert Levels in Database/API

[franTarkenton]

Describe the task Currently alert levels are being defined in the html associated with the basin / alert level component. These values should originate in the database

Acceptance Criteria

• [x] Define a new database fixture that will create the tables and load the data for alert levels... see below for valid alert levels
• [x] Create an end point that will serve this data
• [x] Modify the Alert data structure so that the alert levels are related to this table preventing any undefined levels from making it into the data.
• [ ] Modify the frontend component (basin-lvl-component) so that it retrieves these value from the api

Additional context

• Alert Levels ['High Streamflow Advisor', 'Flood Watch', 'Flood Warning']

[franTarkenton]

initial pr: https://github.com/bcgov/nr-rfc-alertauthoring/pull/75

pr creates new end point for the alert levels