Board refactor - Decouple boardsStore from GraphQL boards [RUN AS-IF-FOSS]

What does this MR do?

Duplicate issue_card_inner and issue_time_estimate components to decouple GraphQL boards from boardsStore.

Simplify VueX state by removing REST API endpoints.

Deprecated components are used on classic REST boards. New versions of said components are used on Swimlanes (Group by Epic dropdown on boards) and on classic boards behind :graphql_board_lists feature flag.

Screenshots (strongly suggested)

No visual changes

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• 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 #292877 (closed)