doc: fix indentation for prometheus config example

[sgomezvillamor]

Description

Fixes indentation in doc for prometheus config.

Considering the fix, no issue has been created.

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as
  expected)
• This change requires a documentation update

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How Has This Been Tested?

TBH Not tested

Checklist:

• I have followed the
  CONTRIBUTING doc and the
  style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works, and I have added a
  changeset using yarn changeset that bumps the version
• New and existing unit tests and linter rules pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Further comments

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[sgomezvillamor]

Just realized someone else already fixed this in master, so closing