Remove all uses of client_id and use a hashed telemetry ID

[crankycoder]

The telemetry ID is being deprecated in favor of a sha256 hashed ID.

Rename variables from client_id toclient_hash in taar for clarity.

Update all ETL jobs in python_mozetl related to TAAR to compute and use hashes instead of raw telemetry client ID.

[crankycoder]

Coordinate with @ddurst regarding the particular HTTP header naming and encoding of the sha hash

[crankycoder]

This code has landed in python_mozetl as of mozilla/python_mozetl#267

The relevant patch on the TAAR application code to convert from a UUID to a hashed telemetry ID is included in #128

See line:

taar/taar/plugin.py

Line 38 in e4efb74

@app.route("/v1/api/recommendations/<hashed_client_id>/", methods=["GET", "POST"])

[crankycoder]

Hashed client ID landed in f279c25.

Tests were updated in 32a3e64