feat(mercurius): add mercurius hooks

[tugascript]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

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

What is the current behavior?

There is no way to add Mercurius Hooks into the Mercurius GraphQL Driver

What is the new behavior?

Adds an optional object with the possible hooks that can be added to mercurius.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[Tony133]

I think it is an interesting feature, I hope it will be added 🙌

[kamilmysliwiec]

There's a bunch of new conflicts that arised after I merged your other PR @tugascript (plugins support) 😢

[tugascript]

There's a bunch of new conflicts that arised after I merged your other PR @tugascript (plugins support) cry

Yeah I expected that, I will rebase the other PR to this one

[kamilmysliwiec]

Note:

This test should be already fixed on master

[tugascript]

Note:

This test should be already fixed on master

Yeah somewhere on the rebase the tests were not copied I am rebasing everything again :')

[tugascript]

@kamilmysliwiec done rebasing could you double check if the tests are ok before merging, they seem in sink, but with rebasing twice, I can have weird behaviour