feat(core): add support for concurrency checks

[B4nan]

As opposed to version fields that are handled automatically, we can use
concurrency checks. They allow us to mark specific properties to be included
in the concurrency check, just like the version field was. But this time, we
will be responsible for updating the fields explicitly.

When we try to update such entity without changing one of the concurrency fields,
OptimisticLockError will be thrown. Same mechanism is then used to check whether
the update succeeded, and throw the same type of error when not.

@Entity()
export class ConcurrencyCheckUser {

  // all primary keys are by default part of the concurrency check
  @PrimaryKey({ length: 100 })
  firstName: string;

  // all primary keys are by default part of the concurrency check
  @PrimaryKey({ length: 100 })
  lastName: string;

  @Property({ concurrencyCheck: true })
  age: number;

  @Property({ nullable: true })
  other?: string;

}

Closes #1638

[codecov-commenter]

Codecov Report

Merging #2437 (e9287cd) into master (209719d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #2437   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          188       188           
  Lines        10724     10747   +23     
  Branches      2445      2451    +6     
=========================================
+ Hits         10724     10747   +23     

Impacted Files	Coverage Δ
packages/core/src/decorators/Property.ts	100.00% <ø> (ø)
packages/core/src/metadata/MetadataDiscovery.ts	100.00% <100.00%> (ø)
packages/core/src/typings.ts	100.00% <100.00%> (ø)
...ckages/core/src/unit-of-work/ChangeSetPersister.ts	100.00% <100.00%> (ø)
packages/knex/src/AbstractSqlDriver.ts	100.00% <100.00%> (ø)

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