Introduce `ClientAppException` #8666

Job	Run time
Build, test and upload wheel	1m 31s
Framework / bare	3m 2s
Strategy / FedMedian	1m 13s
Framework / bare-https	1m 22s
Strategy / FedTrimmedAvg	1m 26s
Framework / jax	1m 57s
Strategy / QFedAvg	1m 26s
Framework / pytorch	2m 51s
Strategy / FaultTolerantFedAvg	1m 23s
Framework / tensorflow	3m 5s
Strategy / FedAvgM	1m 24s
Framework / tabnet	2m 53s
Strategy / FedAdam	1m 40s
Framework / opacus	4m 30s
Strategy / FedAdagrad	1m 30s
Framework / pytorch-lightning	2m 46s
Strategy / FedYogi	1m 22s
Framework / scikit-learn	2m 34s
Framework / fastai	4m 2s
Framework / pandas	1m 46s
	43m 43s

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