Triage package v2.0 with customer bugs and missed SLO bugs

## Background

We are making progress in lowering the time to resolve bugs and increasing awareness.

Its time for an iteration on the content and the structure of the triage content. 
## Current structure

We currently have 3 sections. 

Examples 
* https://gitlab.com/gitlab-org/gitlab-ee/issues/12050
* https://gitlab.com/gitlab-org/gitlab-ee/issues/12042

1. ~feature issues with no milestone and we request that product managers add a milestone to them.
1. ~bug with ~frontend issues with no severity and priority labels. We then ask the ~frontend manager to schedule them.
1. ~bug with with no severity and priority labels. We then ask the ~frontend manager to schedule them.

## Improvements 
1. [x] With Product Managers grooming their features continuously we should consider changing section `1.` to narrow down only ~feature with ~customer. Continue to ask them to be scheduled.
1. [x] With ~Quality handling triage level 1 which includes adding a severity label, we should change section `2.` and `3.` to just ~bug without a milestone. Ask the EM to ensure that the priority is correct or set and schedule a milestone. Maintain 15 max count and prioritize ~bug with ~customer first. https://gitlab.com/gitlab-org/quality/triage-ops/merge_requests/140
1. [x] Include a report on bugs that is past their SLO https://gitlab.com/gitlab-org/quality/triage-ops/issues/137
1. [x] Include heat map on all ~bug for that area. https://gitlab.com/gitlab-org/quality/triage-ops/issues/166
1. [x] Update handbook triage package information.

## Format

Hi, `PM_PLACEHOLDER` `FE_EM_PLACEHOLDER` `BE_EM_PLACEHOLDER`
This is a group or stage level triage package that aims to summarize the feature proposals and bugs which have not been scheduled or triaged. For more information please refer to the handbook:
 - https://about.gitlab.com/handbook/engineering/quality/guidelines/triage-operations/#current-packages

Scheduling the workload is a collaborative effort by the Product Managers and Engineering Managers for that group. Please work together to provide a best estimate on priority and milestone assignments. For each issue please:
 - Determine if the issue should be closed if it is no longer relevant or a duplicate.
 - If it is still relevant please assign either a best estimate versioned milestone, the %Backlog or the %"Awaiting further demand" milestone.
 - Specifically for ~bug, if there is no priority or clarity on a versioned milestone, please add a Priority label. Priority labels have an estimate SLO attached to them and help team members and the wider community understand roughly when it will be considered to be scheduled.
   - `LINK_TO_PRIORITY_DEFINITION`
 - Once a milestone has been assigned please check off the box for that issue.
 - Please work with your team to complete the list by the due date set.


### Heat map report

Here is a heat map report on the distribution of open ~bug for your area.

```
Add heatmap
```

### Feature Proposal section

For the following feature proposals. Please either close or assign either a versioned milestone, the %Backlog or the %"Awaiting further demand" milestone.

#### Unscheduled ~feature with ~customer 

``` 
Lists customer feature proposals with no milestones
Limit: 15 issues
```
#### Unscheduled ~feature (non customer)

```
Lists feature proposals with no milestones
Limit: 15 issues
```

### Bug section

For the following bugs. Please either close or assign either a versioned milestone, the %Backlog or the %"Awaiting further demand" milestone and ensure that a priority label is set.

#### Unscheduled ~frontend ~bug with ~customer 

```Lists customer bugs for frontend with no milestone
Limit: 15 issues
```
#### Unscheduled ~frontend ~bug (non customer) 

```Lists bugs for frontend with no milestone in the project
Limit: 15 issues
```

#### Unscheduled ~bug with ~customer 

```Lists customer bugs without frontend with no milestone
Limit: 15 issues
```

#### Unscheduled ~bug (non customer) 

```Lists bugs without frontend with no milestone
Limit: 15 issues
```

#### ~bug with Missed SLO target section

```Lists bugs that have passed their priority related SLO threshold
Limit: P1 and P2
```

Story points: 7.0