Display downstream pipeline errors in upstream pipelines (UX improvement)
### Summary
When triggering downstream pipelines they can error out. We should be able to display these errors in the upstream bridge job.
### Proposal
We can reach failure reasons of downstream pipelines via `Ci::Bridge#sourced_pipelines`.
However, we don't always create downstream pipelines. Examples:
- https://gitlab.com/gitlab-org/gitlab/-/blob/12-9-stable-ee/app/services/ci/create_cross_project_pipeline_service.rb#L52
After implementing #213666, in this issue, we need store failure reason information of downstream pipelines in bridges. (More discussions about it: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/28120#note_312091893)
Then we can have this behavior:
---
We also need to add failure reason for strategy:depend situations. We may do this in another issue/MR.
Discussion: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/28120#note_318999395
> I would also consider adding `downstream_pipeline_failed` failure reason to a the list of failure reasons supported by `Ci::Bridge`. It seems like a small effort, and might improve the situation here significantly. We probably would need to add this to `self.drop!(...)` in `Ci::Bridge#inherit_status_from_downstream`
---
<details>
<summary>Old Proposal</summary>
1. Persist all pipeline creation errors in `Ci::Pipeline` model. Maybe we can reuse `Ci::Pipeline#yaml_errors` and rename it to `Ci::Pipeline#creation_errors`?
1. When creating a downstream pipeline we now persist always the association between bridge job and downstream pipeline, so we can always reference the downstream pipeline from the bridge job.
1. Change `Gitlab::Ci::Status::Build::Failed#failure_reason_message` to append related downstream pipeline errors if `failure_reason_message` is called to display bridge job errors.
We could look into changing the `failure_reason_message` to append any additional errors from the downstream pipeline.
```ruby
class Ci::Status::Build::Failed
def failure_reason_message
messages = []
messages << self.class.reasons.fetch(subject.failure_reason.to_sym)
messages += subject.additional_errors
messages.join(', ')
end
end
class Ci::Bridge
def additional_errors
return [] unless failure_reason == 'downstream_bridge_pipeline_creation_failed'
# this is not performant and queries need to be optimized
sourced_pipelines.map do |source_pipeline|
source_pipeline.pipeline.yaml_errors
end
end
end
class Ci::Build
def additional_errors
[]
end
end
```
</details>
<details>
<summary>Technical Background</summary>
```
When triggering a downstream pipeline with a bridge job - if the downstream pipeline creation errors out (e.g. an invalid YAML config), the relationship between the bridge job and the downstream pipeline is not saved.
This is because the relation is being added in the `Seed` pipeline chain step and the chain is broken in `Confing::Content` or `Config::Process` which comes before `Seed`.
This is required for displaying the downstream creation errors in upstream bridges.
```
This was resolved with https://gitlab.com/gitlab-org/gitlab/issues/207234
</details>
### Use cases to solve
- https://gitlab.com/gitlab-org/gitlab/issues/204378
- https://gitlab.com/gitlab-org/gitlab/issues/198354
issue