feat(cypress): add "match" custom assertion for subject, body, adresses, and headers

[Kocal]

Q	A
Bug fix?	no
New feature?	yes
Tests pass?	yes
Fixed tickets	#...

Added the possibility to match subject, body, addresses, and headers:

expect(messageEvents.events[0]).to.have.subject.match(/^Hello /);
expect(messageEvents.events[0]).to.have.subject.not.match(/^Goodbye/);

expect(messageEvents.events[0]).to.have.body('text').match('[a-z]+');
expect(messageEvents.events[0]).to.have.body('text').not.match('[a-z]+');

expect(messageEvents.events[0]).to.have.body('html').match('[a-z]+');
expect(messageEvents.events[0]).to.have.body('html').not.match('[a-z]+');

expect(messageEvents.events[0]).to.have.header('From').match(/[a-z]+@example.com/);
expect(messageEvents.events[0]).to.have.header('From').not.match(/[a-z0-9]+@example.com/);

expect(messageEvents.events[0]).to.have.address('From').match(/[a-z]+@example.com/);
expect(messageEvents.events[0]).to.have.address('From').not.match(/[a-z0-9]+@example.com);