Implement pessimistic lock support

[beikov]

Currently only optimistic locking is implemented, but the annotation model already supports configuring pessimistic locking. We need to implement the locking correctly and add tests.
As part of this, we should also add an API for allowing to override the lock mode via EntityViewSetting. Also think of how other lock modes like e.g. SKIP_LOCKED could be supported.

[david-kubecka]

Any update or possibly even ETA? We would like to use LockMode.PESSIMISTIC_WRITE.

[beikov]

Sorry, no ETA yet, but you can look into it if you want. I guess a good start would be to express the expectations in a draft PR as tests in a first round. The EntityViewSetting API for applying lock modes can be as simple as void setLockMode(LockMode) + void setLockMode(LockMode, String attributePath). Might be worth adding our own LockMode enum though.