Fix get_countour_plot() not plotting all trials

[ligerlac]

This fixes a bug where get_countour_plot() plots all but the last trial. The corresponding issue is here: #2221.

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[ligerlac]

AxClient.get_contour_plot() plots the training data of the model of the generation strategy as 'in-sample':

Ax/ax/plot/helper.py

Line 189 in 2967164

observations = model.get_training_data()

However, this does not necessarily contain all trials of the experiment. For example, in the code snippet provided in the original issue (#2221 (comment)), the model of the generation strategy is updated when ax_client.get_next_trial() is called. Therefore, the last trial will not be displayed in the contour plot.
Passing all trials as generator_runs_dict like so 3d2eec2 leads to duplicated data points except for the last trial. Alternatively, only trials that are not already present in the training data could be passed. Both solutions, however, result in a plot where the colored contours of the model do not take all displayed data points into account, which might be counter-intuitive.
Another possible solution would be to fit the model one more time before making the plot, ensuring the model is up-to-date with all completed trials. Something similar is done when retrieving the model's predictions here:

Ax/ax/service/ax_client.py

Lines 1186 to 1189 in 2967164

	# Fit model to ensure:
	# - model is instantiated if needed
	# - any new completed trials are fit to the model
	self.fit_model()

But that might be unexpected behavior.
Maybe @mgarrard can comment?