Consider blocking reactive messaging methods using @Transactional

[cescoffier]

Fix #21795

[cescoffier]

The benefit is the following:

before:

    @Incoming("prices")
    @Blocking
    @Transactional
    public void store(int priceInUsd) {
        Price price = new Price();
        price.value = priceInUsd;
        price.persist();
    }

after:

    @Incoming("prices")
    @Transactional
    public void store(int priceInUsd) {
        Price price = new Price();
        price.value = priceInUsd;
        price.persist();
    }

[geoand]

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