Participant is not initialised correctly when loading from JSON

[NoB0]

Update dialogue reader to initialize utterance participant to DialogueParticipant.

Fixes #260

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Unit Test Results

86 tests   86 :heavy_check_mark:  49s :stopwatch:   1 suites    0 :zzz:   1 files      0 :x:

Results for commit f645db09.

:recycle: This comment has been updated with latest results.

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Coverage Report •

File	Stmts	Miss	Cover	Missing
dialoguekit/utils
dialogue_evaluation.py	104	1	98%	96, 154–>162
dialogue_reader.py	66	2	92%	70–>73, 84, 146
tests/utils
test_dialogue_reader.py	29	0	100%
TOTAL	2236	208	89%

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Current Branch	Main Branch