Completed db cleanup

[jo-asplin-met-no]

This change completes the periodic database cleanup by also deleting unreferred rows in tables time_series and geo_point. Calls to the cleanup function are also now triggered from a single goroutine that runs independently of calls to PutObservations().

[github-actions]

API Unit Test Coverage Report

File	Stmts	Miss	Cover	Missing
\_\_init\_\_.py	0	0	100%
datastore_pb2.py	61	48	21%	34–81
datastore_pb2_grpc.py	54	27	50%	15–16, 19, 57–72, 105–107, 112–114, 119–121, 126–128, 132–157, 195, 222, 249, 276
export_metrics.py	10	0	100%
grpc_getter.py	20	11	45%	15–19, 23–26, 30–32, 36–38
locustfile.py	15	15	0%	1–31
main.py	43	7	84%	45, 50, 60, 70–71, 81–82
metadata_endpoints.py	63	29	54%	45–54, 58, 85, 100–216, 220
response_classes.py	5	0	100%
utilities.py	181	56	69%	20, 38, 45, 67–70, 78–89, 94–101, 121, 125, 127, 154, 157, 166, 184–185, 189, 205–210, 215, 219–220, 224–226, 232–240, 250–253, 259–260, 272–276, 299, 304, 317
custom_geo_json
edr_feature_collection.py	6	0	100%
formatters
\_\_init\_\_.py	11	0	100%
covjson.py	57	1	98%	88
geojson.py	17	2	88%	21, 46
openapi
custom_dimension_examples.py	4	0	100%
edr_query_parameter_descriptions.py	11	0	100%
openapi_examples.py	13	0	100%
routers
\_\_init\_\_.py	0	0	100%
edr.py	102	4	96%	350–351, 441–442
feature.py	47	19	60%	99–132, 148–153, 159–181
TOTAL	720	219	70%

API Unit Test Coverage Summary

Tests	Skipped	Failures	Errors	Time
30	0 💤	0 ❌	0 🔥	1.948s ⏱️

[lukas-phaf]

Much cleaner solution! ;-)

And what would a go program be without a channel...