Standardize punctuation and format

This makes `epic_issues` consistent with other tables
using our `RelativePositioning` class

https://gitlab.com/gitlab-org/gitlab-ce/issues/62971

Adds support to EnvironmentsController#metrics_dashboard
for the following params: group, title, y_label
These params are used to uniquely identify a panel on
the metrics dashboard.

Metrics are stored in several places, so this adds
utilities to find a specific panel from the database
or filesystem depending on the metric specified.

Also moves some shared utilities into separate classes,
notably default values and errors.

Send a `persist_filter: false` param to backend when
opening links to notes and auto-switching to show
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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.

- 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

API endpoints for requesting container repositories
and container repositories with their tag information
are enabled for users that want to specify the group
containing the repository rather than the specific project.

Also removes unnecessary methods causing extra queries

Moving of neighbour items was done recursively - this
was extremely expensive when multiple items had to be moved.

This change optimizes the code to find nearest possible gap where
items can be moved and moves all of them with single update query.

Add outbound setting for system hooks

See merge request gitlab-org/gitlab-ce!31177