model.py: save payload as text instead of encoded UTF-8
model.py: save payload as text instead of encoded UTF-8

The website does not decode text. Without this change using the Record
initializer directly, such as in Record.create, would result in payload
text not being human readable.

Signed-off-by: California Sullivan <2c9b9344ce0c0bd803b8397085f0d9381eef7902@intel.com>

alexjch/telemetrics-backend,alexjch/telemetrics-backend,alexjch/telemetrics-backend,alexjch/telemetrics-backend