This reverts merge request !29832

A Noteable doesn't have a group directly, unless it's an epic - we need
to look for the project's group to find the right email address.

Make HTML and text emails for new issues uniform and add the mail to mailer previews

Closes #58065

See merge request gitlab-org/gitlab-ce!29886

Fix copying a single line from Firefox

Closes #63406

See merge request gitlab-org/gitlab-ce!29832

Uniform new_issue_email html and text emails
Uniform note_email html and text emails
Uniform new_merge_request_email html and text emails

Since Kubernetes is creating the Secret and token asynchronously it is
necessary that we implement some delay or retrying logic to avoid a race
condition where we fetch a Secret before the token is even set. There
does not appear to be any way for us to force it to be set with any
synchronous API call so retrying seems to be the only option.

This commits adds support for metrics dashboards
for embedding. If the flag 'embedded' is provided
to the environments/id/metrics_dashboard endpoint,
the response will be suitable for embedding in
issues or other content.

This is a precursor for support for embedding
metrics in GFM.

Fix N+1 problem in `JobsController#index`

See merge request gitlab-org/gitlab-ce!29839

This backports to CE changes to allow the EE model
DesignManagement::Repository to override the #attributes_at method to
provide its own git attributes.

The #attributes_at method was freely available, as it's never called by
anything in the app. It looks like the code that called it got
refactored out of existence in ca66a04f. It was still being called in a
spec
https://gitlab.com/gitlab-org/gitlab-ce/blob/85b29c1c2fa3b94d7371cf454c485457a0756cb1/spec/services/files/create_service_spec.rb#L40
which I've left because with the change in Lfs::FileTransformer in fact
is now again the perfect test!

See EE MR
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14017

And these comment threads
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/13894#note_178002089
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/13894#note_178049984

# Conflicts:
#   spec/lib/gitlab/ci/ansi2html_spec.rb