Merged PR 1519739: Fix mongorestore for collections with text indexes

### Does this PR have any customer impact?
Yes

### Type (Feature, Refactoring, Bugfix, DevOps, Testing, Perf, etc)
Bugfix

### Does it involve schema level changes? (Table, Column, Index, UDF, etc level changes)
No

### Are you introducing any new config? If yes, do you have tests with and without them being set?
No

### Release Note (Refer [Template](../docs/release_notes/pgmongo_template.md))

### Description
To be updated. Meanwhile, please see the text_indexes.md file in the changeset for what motivated this change, and also a brief description of the same.

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#### AI description  (iteration 1)
#### PR Classification
Bug fix

#### PR Summary
This pull request fixes the `mongorestore` functionality for collections with text indexes by handling the `_fts` and `_ftsx` metadata terms correctly.
- Added documentation on text indexes in `PGMongo` in `docs/pgmongo/design_docs/data_plane/indexing/text_indexes.md`.
- Updated `oss/pg_helio_api/src/metadata/index.c` to handle `_fts` and `_ftsx` terms in index specifications.
- Modified `oss/pg_helio_api/src/commands/create_indexes.c` to correctly generate index expressions and handle text index options.
- Updated `docs/pgmongo/design_docs/data_plane/indexing/toc.yml` to include the new text indexes documentation.

Author: Amit Prabhudesai