Add TimescaleDB integration tests

[davydog187]

From @akoutmos in slack

akoutmos - We should also add an issue for integration tests in CI

the assert_sql assertion is good for unit testing, but would be great to get some real TimescaleDB integration tests to validate that the functions not only produce expected SQL, but also return the expected results

💯 that we should have integration tests here. The main issue will be finding a way to have ecto migrations without shipping them in the library. We may just need a publishing script that wipes the priv directory when we do mix hex.publish

[davydog187]

I just tried writing some tests for the migration functions, and realizing that we can only test these via integration tests.

defmodule Timescale.MigrationTest do
  use Timescale.SQLCase

  import Timescale.Migration

  alias TimescaleApp.Table

  test "add_compression_policy/2 generates a valid query" do
    assert_sql(
      add_compression_policy(:my_table, "5 minutes"),
      ~s[SELECT last(m0."a", m0."timestamp") FROM "my_table" AS m0]
    )
  end
end

will yield

  1) test add_compression_policy/2 generates a valid query (Timescale.MigrationTest)
     test/timescale/migration_test.exs:8
     ** (RuntimeError) could not find migration runner process for #PID<0.326.0>
     code: add_compression_policy(:my_table, "5 minutes"),
     stacktrace:
       (ecto_sql 3.8.3) lib/ecto/migration/runner.ex:304: Ecto.Migration.Runner.runner/0
       (ecto_sql 3.8.3) lib/ecto/migration/runner.ex:129: Ecto.Migration.Runner.execute/1
       test/timescale/migration_test.exs:10: (test)