feat(typed-cqrs): use symbol field to store type of query

[Papooch]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs-architect/typed-cqrs/blob/master/CONTRIBUTING.md#git-guidelines (probably yes, but the link is broken)
• Tests for the changes have been added (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Updates typescript (in order to use symbols), while adding dependency to itself so that the examples type check correctly after npm run build without needing to use link.
• The type of commands and queries is now stored in a symbol field, which makes it invisible in consumer code (unlike previous implementation based on a random name)

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

The same as before, only now there's no random property visible on the query.

Issue Number: N/A

Does this PR introduce a breaking change?

[ ] Yes
[x] Maybe, if someone depended on the random property, which I doubt.
[ ] No

Fixes #4

[ajfranzoia]

Is this unmaintained?

[Sikora00]

Why we need it?

[Papooch]

We don't, I can remove it from the PR if you want, but this removes the need to call npm link in order for the examples to typecheck correctly.

[Papooch]

Removed and rebased

[Sikora00]

Cool! amazing contribution @Papooch
@ajfranzoia it hurts...