Refactor OpenSearch model into builder services

[jazairi]

Why these changes are being introduced:

The OpenSearch model has become unwieldy, and will continue to grow as we add semantic search
functionality.

Relevant ticket(s):

• USE-372

How this addresses that need:

This breaks out the OpenSearch logic into multiple builder models: Filter Builder and Lexical Query
Builder (with Semantic Query Builder to come
later). This refactor is intended to improve
maintainability.

Side effects of this change:

• The OpenSearch model still retains some query building logic, most notably search highlights.
  We could consider creating a very small
  HighlightBuilder service if we want to commit to
  this architectural pattern.
• As discussed in the ADR for this change, we will not be implementing the 'Strategy' selector model
  at this time. That change will come later, once
  semantic search has been implemented.

Developer

• All new ENV is documented in README
• All new ENV has been added to Heroku Pipeline, Staging and Prod
• ANDI or Wave has been run in accordance to
  our guide and
  all issues introduced by these changes have been resolved or opened as new
  issues (link to those issues in the Pull Request details above)
• Stakeholder approval has been confirmed (or is not needed)

Code Reviewer

• The commit message is clear and follows our guidelines
  (not just this pull request message)
• There are appropriate tests covering any new functionality
• The documentation has been updated or is unnecessary
• The changes have been verified
• New dependencies are appropriate or there were no changes

Requires database migrations?

NO

Includes new or updated dependencies?

NO