[EngSys] Docs release jobs should only run if executed from public repo

Docs release jobs (e.g. update docs.ms metadata, publish to github.io docs) should only run when the pipeline is being executed from a public repo (i.e. repo name does not have `-pr` in the suffix). After reviewing use of similar clauses in other repos, let's use this construction for the condition: ```yaml ne(variables['Build.Repository.Name'], 'Azure/azure-sdk-for-cpp-pr') ```