Feat: JH custom global footer

What does this MR do?

This is a JH related feature

@meks @leipert

Even though this is a JH feature for now, but I'd like to make it here as a reusable entry so that if anyone wants to add something here can use it.

Description

Per regional policy, we need to put some governmental records on the UI like the screenshot shows, but for current page implementation we weren't able to do that, so we need to add an entry here so that it can render the custom footer for our clients.

Since this should be inside content-wrapper element, we can not use the GitLab provided footer config in the Admin dashboard (because it doesn't meet the UI requirement). So here we put a conditional rendering partial for rendering jh/view/shared/global_footer(the name is arbitrary for now, we can discuss that), after adding this entry, we can get our customized footer rendered into the DOM for every single page(except those campaign page I assume).

• Add a conditional footer into _page partial.

Screenshots or Screencasts (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