Add milestone wildcard filters and MR count to issues page refactor

What does this MR do?

This MR adds features to the issues page refactor which were recently added to the backend GraphQL API:

• Adds the ability to filter issues by milestone None, Any, Upcoming, and Started on the issues page refactor (tested in filter_issues_spec.rb#L360)
• Adds a merge request count on the issues card (tested in issuable_list_spec.rb#L59)

This change is part of the issues page refactor #322755 (closed), behind feature flag vue_issues_list defaulted to off. The feature specs will be run against the issues refactor instead of the issues Haml page in !61123 (closed)

Screenshots or Screencasts (strongly suggested)

Screen_Recording_2021-08-03_at_4.49.10_pm

How to setup and validate locally (strongly suggested)

1. Enable the vue_issues_list feature flag

   Feature.enable(:vue_issues_list)

2. Visit the issues page http://127.0.0.1:3000/h5bp/html5-boilerplate/-/issues/
3. Select Milestone = None etc in the filter search bar.

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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 #322755 (closed)