Streams support POC

[rStelmach]

Summary

Add a new elasticstack_kibana_stream Terraform resource backed by the main kbapi Kibana client, plus a small internal condition model and Streams API helpers, to validate the first end‑to‑end integration between Terraform and Streams.
This POC focuses on group streams, base‑stream creation, and a read‑only view of ingest, without committing yet to a final public Terraform schema for all Streams features.

What this PR changes

• Streams API helpers (internal/clients/kibana_oapi/streams.go)

  • Wrap the existing kbapi.ClientWithResponses on top of the Kibana HTTP client.
  • Provide focused helpers for:
    • EnableStreams / DisableStreams (POST /api/streams/_enable|_disable),
    • GetStreamJSON, PutStreamRaw, DeleteStream (with the "Expected undefined, received null" quirk handled),
    • GetStreamIngestJSON / PutStreamIngest,
    • GetStreamGroupJSON / PutStreamGroup.

• New Terraform resource: elasticstack_kibana_stream (internal/kibana/streams)

  • Registered in provider/plugin_framework.go via streams.NewResource.
  • Schema + models:
    • Top‑level: id, name, space_id, description, type, create_if_missing.
    • group { members, metadata, tags } – managed via /api/streams/{name}/_group.
    • ingest { type } – computed, read‑only from /api/streams/{name}/_ingest in this POC.
  • CRUD behavior:
    • Group streams: optionally create the base stream, upsert _group, round‑trip members/metadata/tags, and delete via DELETE /api/streams/{name} with quirks handled.
    • Ingest streams: read‑only (Terraform reads _ingest but does not write it yet) .

• Internal condition expression model (internal/kibana/streams/conditions.go)

  • Small internal tree (Condition, FieldComparison, And, Or) plus MarshalCondition helper.
  • Unit tests in conditions_test.go verify JSON output for simple and nested trees.

Testing

Kibana's side :

• generate logs

Terraform side

• Unit tests:
  • go test ./internal/kibana/streams/... (condition model + flatten/expand helpers).
• Manual POC validation:
  • Adjust kibana url in new main.tf
  • Build the provider: make build.
  • cd streams then run:
    • terraform init
    • terraform apply
  • Confirm:
    • Group streams: base stream creation via create_if_missing = true, _group upsert, and round‑trip of members / metadata / tags.
    • Ingest streams: read‑only ingest behavior (ingest.type populated from _ingest, no writes to _ingest).