Use less expensive index_options

What does this MR do?

Currently the Elasticsearch mapping stores a lot of extra information for each term it stores. This is replaced with less expensive options (like positions instead of offsets or even docs instead of offsets when highlighting is not needed and scoring is less of an issue).

Original issue

Testing different options on a project from gitlabhq_export.tar.gz

Options	Size, MB	%
offsets (current)	808.2	100.00%
positions	561.53	69.48%	-30.52%
mixed	512.38	63.40%	-36.60%

• there is no noticeable difference in searching speed between those options

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

Closes #28085 (closed)