Continuous Aggregate support

[davydog187]

Look into what we want to support in Continuous Aggregates.

Since setting a continuous aggregate up involves materialized view syntax, we may want to just have documentation for setting up CAs in Ecto, and then add the following functions

• https://docs.timescale.com/api/latest/continuous-aggregates/add_continuous_aggregate_policy/
• https://docs.timescale.com/api/latest/continuous-aggregates/refresh_continuous_aggregate/
• https://docs.timescale.com/api/latest/continuous-aggregates/remove_continuous_aggregate_policy/