Add depth limit validator

[jkimbo]

Description

Adds a python port of https://github.com/stems/graphql-depth-limit

Also allow passing custom validators to execute_sync and execute.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation

Issues Fixed or Closed by This PR

• Add utilities for preventing malicious queries #960

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

This release adds a query depth limit validation rule so that you can guard
against malicious queries:

import strawberry
from strawberry.schema import default_validation_rules
from strawberry.tools import depth_limit_validator


# Add the depth limit validator to the list of default validation rules
validation_rules = (
  default_validation_rules + [depth_limit_validator(3)]
)

result = schema.execute_sync(
    """
    query MyQuery {
      user {
        pets {
          owner {
            pets {
              name
            }
          }
        }
      }
    }
    """,
    validation_rules=validation_rules,
  )
)
assert len(result.errors) == 1
assert result.errors[0].message == "'MyQuery' exceeds maximum operation depth of 3"

---

Here's the preview release card for twitter:

Here's the tweet text:

Another great feature by @jonnykim! Now we are able to pass
custom validators when executing GraphQL queries. And we
already have one built-in validator to disable queries by depth!

Check it out here 👉 https://github.com/strawberry-graphql/strawberry/releases/tag/(next)

[codecov]

Codecov Report

Merging #1021 (19c6662) into main (776b98f) will increase coverage by 0.11%.
The diff coverage is 98.61%.

@@            Coverage Diff             @@
##             main    #1021      +/-   ##
==========================================
+ Coverage   97.43%   97.55%   +0.11%     
==========================================
  Files          81       82       +1     
  Lines        3044     3110      +66     
  Branches      420      440      +20     
==========================================
+ Hits         2966     3034      +68     
+ Misses         44       42       -2     
  Partials       34       34              

[DoctorJohn]

Nice work, I'm very excited for this. I added a couple of small comments, just things that came to my mind :)

[jkimbo]

Thanks for the review @DoctorJohn , I'll get those changes in as soon as I can.

[DoctorJohn]

LGTM 👍

[patrick91]

💯