ActionView::Template::Error: PG::QueryCanceled: ERROR: canceling statement due to statement timeout

Customer has more than 50 scheduled pipeline before we implemented the scheduled pipeline limit. Now they get 500 errors every time they visit the page. They can use the API to view the scheduled pipeline and delete them for now but we should show a better error message and provide suggestion for the workaround on the page instead of 500 error.

https://sentry.gitlab.net/gitlab/gitlabcom/issues/1818216/?referrer=gitlab_plugin

PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

  active_record/connection_adapters/postgresql_adapter.rb:675:in `exec_params'
    @connection.exec_params(sql, type_casted_binds)
  active_record/connection_adapters/postgresql_adapter.rb:675:in `block (2 levels) in exec_no_cache'
    @connection.exec_params(sql, type_casted_binds)
  active_support/dependencies/interlock.rb:48:in `block in permit_concurrent_loads'
    yield
  active_support/concurrency/share_lock.rb:187:in `yield_shares'
    yield
  active_support/dependencies/interlock.rb:47:in `permit_concurrent_loads'
    @lock.yield_shares(compatible: [:load]) do
...
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ActiveRecord::QueryCanceled: PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

ActionView::Template::Error: PG::QueryCanceled: ERROR:  canceling statement due to statement timeout