Exhaustively test relative positioning logic

See merge request gitlab-org/gitlab!41967

Guide for adding a new service component to GitLab

See merge request gitlab-org/gitlab!34965

Add Gitpod Integration – Add Gitpod buttons to start cloud dev environments for GitLab projects

Closes #228893

See merge request gitlab-org/gitlab!37985

- Introduces :gitpod feature flag
- A later MR will handle adding to the MR page

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/37985

Add group_level_integrations feature flag info

See merge request gitlab-org/gitlab!42454

Remove job logs from notification e-mails

See merge request gitlab-org/gitlab!42395

Fix daemon memory killer jobs hash thread safety issue

Closes #249519

See merge request gitlab-org/gitlab!42468

TEST MR - This MR won't be merged

See merge request gitlab-org/security/gitlab!941

Add more detail for Praefect auto reconciliation

See merge request gitlab-org/gitlab!42304

TEST MR - This MR won't be merged

See merge request gitlab-org/security/gitlab!937

Update Gitaly version

See merge request gitlab-org/gitlab!42490

Update offline docs for AR

See merge request gitlab-org/gitlab!41381

Fix background migration temporary class definition

See merge request gitlab-org/gitlab!42413

Create placeholder model in CE for Vulnerability

See merge request gitlab-org/gitlab!42147

This change adds new placeholder model for Vulnerability and moves
previously created model to EE::Vulnerability module.

This is a bit more acceptable: just under 2min, and 1175 examples.

This includes a bunch of optimizations (avoiding re-creating issues,
being very careful about resets) that means we can run over a range of
size 6 (2606 examples) in about 4min 30s.

We want the `new_item` to be a new, unplaced item.

We have made `move_sequence` a private method, so we need to call it
using send.

The RelativePositioning::Range class is reponsible for inferring
the other end of ranges, testing if the range is open and detecting
if an object is contained within the range (allowing us to avoid some
operations).

This divides up the relative_positioning class specs into the
appropriate places in the lib tree

This moves Mover, ItemContext and Gap into the lib tree where they can
be used separately from the app code.

The changes tested here are to see if in EE projects in the same groups
count as part of the same relative positioning set. We do not need to
test every method - just the scoping query.

Frankly a bunch of the movement tests could also be removed, but they
are all calling public methods so it is fine for them to test the
interface.

This is now part of the usage instructions in the relative positioning
shared examples.

Since classes that include RelativePositioning no longer can override
low-level implementation methods to hook into internal details, this
means that catching query timeouts and other failures systematically is
no longer straightforward.

This change allows classes to implement a new callback hook:
`#could_not_move`, which is called with an exception if any of the
movement methods times out.

This involves custom handling for polymorphic models, and null-safety.

Hetrogenous sets of items need to override a couple of methods