chore(deps): upgrade mercurius gateway to v2.1.0

[ctkc]

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: Dev and peer dependency upgrade.

What is the current behavior?

Mercurius Gateway has some new options available and those are not reflected by @nestjs/mercurius because of the current version.

Issue Number: N/A

What is the new behavior?

There is no new behavior from @nestjs/mercurius side. You can find Mercurius Gateway changes here

Does this PR introduce a breaking change?

• Yes
• No

According to the changelogs there are no breaking changes

Other information

• I had to downgrade the eslint-plugin-prettier to latest v4 because it is not compatible with the current Prettier version (v2.8.8) and it's breaking ESLint. Seems like it was upgraded here by the robot. We have to either upgrade Prettier to v3 or keep eslint-plugin-prettier v4.
  Please, let me know if you want me to upgrade Prettier to v3 instead which likely will introduce changes in the format of the files.
• There were two other files modified when I run Prettier

NOTE: The build is failing because the yarn.lock file was modified due to the upgrades and the CI is running install with --frozen-lockfile