Fix assorted links in the docs

See merge request gitlab-org/gitlab-ce!31559

Fix links as discovered by the lint in the docs project

Add support for Content-Security-Policy

Closes #65330

See merge request gitlab-org/gitlab-ce!31402

Provide separate namespaces for each project environment

See merge request gitlab-org/gitlab-ce!30711

Kubernetes deployments on new clusters will now have
a separate namespace per project environment, instead
of sharing a single namespace for the project.

Behaviour of existing clusters is unchanged.

All new functionality is controlled by the
:kubernetes_namespace_per_environment feature flag,
which is safe to enable/disable at any time.

Follow-up: Tweak line to improve badge placement

Closes #65417

See merge request gitlab-org/gitlab-ce!31528

Follow-Up: Change code blocks to shell type

Closes #65605

See merge request gitlab-org/gitlab-ce!31526

Resolve "Use Gitlab::HTTP in PrometheusClient instead of RestClient"

Closes #60024

See merge request gitlab-org/gitlab-ce!31053

- Closes #60024

- Change PrometheusClient.new to accept a base url instead of an
  already created RestClient

- Use Gitlab::HTTP in PrometheusClient instead of creating RestClient
  in PrometheusService

- Move http_options from PrometheusService to
  PrometheusClient (follow_redirects: false)

- ensure that base urls don't have the trailing slash

- Created a `PrometheusClient#url` method that might not be strictly
  required

- Change rescued exceptions from RestClient::* to
  HTTParty::ResponseError where possible and StandardError for the
  rest

A nonce-based Content-Security-Policy thwarts XSS attacks by allowing
inline JavaScript to execute if the script nonce matches the header
value. Rails 5.2 supports nonce-based Content-Security-Policy headers,
so provide configuration to enable this and make it work.

To support this, we need to change all `:javascript` HAML filters to the
following form:

```
= javascript_tag nonce: true do
  :plain
    ...
```

We use `%script` throughout our HAML to store JSON and other text, but
since this doesn't execute, browsers don't appear to block this content
from being used and require the nonce value to be present.

Docs - Update link in SSL_TLS Certificates Page to Let's Encrypt Intergration

See merge request gitlab-org/gitlab-ce!30984

Fix nil take regression

Closes #65725

See merge request gitlab-org/gitlab-ce!31554

Default number of GCP nodes to 1

See merge request gitlab-org/gitlab-ce!31497

By defaulting to 3, there is unnecessary cost
involved

Remove GC metrics from performance bar

Closes gitlab-org/quality/nightly#122

See merge request gitlab-org/gitlab-ce!31550

Add committer approval API attribute docs

Closes #61796

See merge request gitlab-org/gitlab-ce!31538

These were disabled in production mode, but that also broke the rest of
the performance bar. As they were only enabled in development mode, we
can just remove them for now.

Update Packer.gitlab-ci.yml to use latest image

See merge request gitlab-org/gitlab-ce!31548

Merge Requests Approvals can be restricted to prevent the merge
request author or merge request committers from self approving. The
author restriction is already available in the API, but the committer
restriction was not.

Prevents showing 2 tooltips in pipelines

Closes #64608

See merge request gitlab-org/gitlab-ce!31521

Update mini_magick to 4.9.5

Closes #65671

See merge request gitlab-org/gitlab-ce!31505

Suggest disabling of NFS delegation not needed for RHEL7 update

See merge request gitlab-org/gitlab-ce!31546

Red Hat finally fixed the NFS server delegation problem that caused the
TEST_STATEID flood. Mention the docs that disabling delegation may
no longer be needed.

Add top navigation analytics link

See merge request gitlab-org/gitlab-ce!30324

Support selective highlighting of lines

See merge request gitlab-org/gitlab-ce!31361

Disable review apps for auto-deploy branches

See merge request gitlab-org/gitlab-ce!31494

Update karma to 4.2.0

Closes #65660

See merge request gitlab-org/gitlab-ce!31495

Improve the performance of viewing deploy keys

Closes #43080

See merge request gitlab-org/gitlab-ce!31384

Make issue boards importable

See merge request gitlab-org/gitlab-ce!31434

Backport productivity analytics migrations

See merge request gitlab-org/gitlab-ce!31298

Resolve "Add point of interest discussions to designs"

See merge request gitlab-org/gitlab-ce!31276

This reverts commit d754beb74fbc06a2c744e15be4aa2831d8cef1c0.

Hides loading spinner after request

Closes #65263

See merge request gitlab-org/gitlab-ce!31478

Alerts dropdown to modal CE2

See merge request gitlab-org/gitlab-ce!31181

Added as EE backport