Add discord and symphony alerts

[timkpaine]

No description provided.

[github-actions]

Test Results

15 tests  +4   14 ✅ +3   6s ⏱️ +4s
 1 suites ±0    1 💤 +1 
 1 files   ±0    0 ❌ ±0 

Results for commit eed8a8b. ± Comparison against base commit 7971571.

[codecov]

Codecov Report

Attention: Patch coverage is 77.04918% with 28 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
airflow_priority/plugins/symphony.py	54.90%	22 Missing and 1 partial ⚠️
airflow_priority/plugins/discord.py	93.47%	2 Missing and 1 partial ⚠️
airflow_priority/tests/test_symphony.py	83.33%	2 Missing ⚠️

Files	Coverage Δ
airflow_priority/common.py	82.60% <100.00%> (+8.69%)	⬆️
airflow_priority/plugins/datadog.py	89.58% <ø> (ø)
airflow_priority/plugins/newrelic.py	86.84% <100.00%> (ø)
airflow_priority/plugins/slack.py	83.33% <100.00%> (ø)
airflow_priority/tests/conftest.py	100.00% <ø> (ø)
airflow_priority/tests/test_discord.py	100.00% <100.00%> (ø)
airflow_priority/tests/test_symphony.py	83.33% <83.33%> (ø)
airflow_priority/plugins/discord.py	93.47% <93.47%> (ø)
airflow_priority/plugins/symphony.py	54.90% <54.90%> (ø)