Draft: Add ci_pipeline_id to pages_deployments

What does this MR do?

Adds the ci_pipeline_id column to the pages_deplyments table. It also adds the pipeline id when creating a Pages deployment.

DB

Up

rake db:migrate
== 20210809054753 AddCiPipelineIdToPagesDeployments: migrating ================
-- add_column(:pages_deployments, :ci_pipeline_id, :integer)
   -> 0.0026s
-- transaction_open?()
   -> 0.0000s
-- foreign_keys(:pages_deployments)
   -> 0.0061s
-- execute("ALTER TABLE pages_deployments\nADD CONSTRAINT fk_689a4298e9\nFOREIGN KEY (ci_pipeline_id)\nREFERENCES ci_pipelines (id)\nON DELETE SET NULL\nNOT VALID;\n")
   -> 0.0038s
-- execute("SET statement_timeout TO 0")
   -> 0.0005s
-- execute("ALTER TABLE pages_deployments VALIDATE CONSTRAINT fk_689a4298e9;")
   -> 0.0064s
-- execute("RESET ALL")
   -> 0.0005s
== 20210809054753 AddCiPipelineIdToPagesDeployments: migrated (0.0306s) =======

Down

❯ rake db:migrate:down VERSION=20210809054753
== 20210809054753 AddCiPipelineIdToPagesDeployments: reverting ================
-- remove_foreign_key(:pages_deployments, {:column=>:ci_pipeline_id})
   -> 0.0063s
-- remove_column(:pages_deployments, :ci_pipeline_id)
   -> 0.0007s
== 20210809054753 AddCiPipelineIdToPagesDeployments: reverted (0.0140s) =======

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How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #208322 (closed)