[Feature] Add require conversation resolution before merging support to github_branch_protection resource

[nantiferov]

Hi there,

GitHub recently added new rule to branch protection, named Require conversation resolution before merging.
go-github already support it: google/go-github#1945, google/go-github#1959

Would be nice to have it in terraform github_branch_protection resource

[nantiferov]

Afaik this feature was implemented in #904
And supported now by github_branch_protection resource, option require_conversation_resolution
https://github.com/integrations/terraform-provider-github/blob/main/website/docs/r/branch_protection.html.markdown

I will close this issue as done. Thank you!