Prohibit creation of automatic ES indices

What does this MR do?

When no index exists yet, yet we turned on "Elasticsearch Indexing", any index call would automatically create an index. However that index does not honor GitLab's setting and mappings, making that index useless.

To fix the problem we started to warn users and we disable "Index all project" button if there is no index available.

We discussed disabling auto_create_index, but it's still not clear when we should do that.

#13717 (closed)

Screenshots

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