Application limit for ES indexed field length

What does this MR do?

Using the plan_limit table we can down store a limit for the maximum size of any fields being indexed in Elasticsearch. This is for #201826 (closed) . Any strings above the length limit will be truncated down to the limit.

We default to 0 which means unlimited so this has no affect for self-managed customers. On GitLab.com we will likely want to set this to around 20k as a sensible upper limit on what we should store.

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

#201826 (closed)