Support separate issues index in create_empty_index rake task

What does this MR do?

Related to #273479 (closed)

Built upon work in: !48334 (merged) and we will merge into this branch to ensure that all of the changes go out at once.

Update the gitlab:elastic:create_empty_index rake task to support separate index for issues. The rake task also supports reclaiming the gitlab-production index name by setting the environment variable SKIP_ALIAS. If that environment variable is set, the separate indices will not be created.

Add new specs and updated some existing ones

Update documentation

Screenshots (strongly suggested)

> bundle exec rake gitlab:elastic:create_empty_index
Index 'gitlab-development-issues-20210104-1311' has been created.
Alias 'gitlab-development-issues' -> 'gitlab-development-issues-20210104-1311' has been created.
Index 'gitlab-development-20210104-1311' has been created.
Alias 'gitlab-development' → 'gitlab-development-20210104-1311' has been created

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