add enr filtering

[nibty]

Please check if what you want to add to go-opera list meets quality standards before sending pull request.

Please provide package links to:

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Make sure that you've checked the boxes below before you submit PR:

• I have added my package in alphabetical order.
• I have an appropriate description with correct grammar.
• I know that this package was not listed before.
• I have added godoc link to the repo and to my pull request.
• I have added coverage service link to the repo and to my pull request.
• I have added goreportcard link to the repo and to my pull request.
• I have read Contribution guidelines, maintainers note and Quality standard.