Added tests for the notifications plugin.

[dblock]

Description

Added tests for the notifications plugin.

The additional docker-compose boots a webhook notifications channel that just responds with {ok: true} to everything.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

Changes Analysis

Commit SHA: 179708b
Comparing To SHA: 6b63759

API Changes

Summary

├─┬Paths
│ └─┬/_plugins/_notifications/configs
│   └─┬GET
│     ├──[➕] parameters (22410:13)❌ 
│     └──[➕] parameters (22404:13)❌ 
└─┬Components
  ├──[➕] parameters (22410:7)
  ├──[➕] parameters (22404:7)
  └─┬notifications._common:RestStatus
    ├──[➕] enum (53262:11)
    ├──[➕] enum (53263:11)
    ├──[➕] enum (53256:11)
    ├──[➕] enum (53257:11)
    ├──[➕] enum (53258:11)
    ├──[➕] enum (53259:11)
    ├──[➕] enum (53260:11)
    ├──[➕] enum (53261:11)
    ├──[➖] enum (53250:11)❌ 
    ├──[➖] enum (53251:11)❌ 
    ├──[➖] enum (53253:11)❌ 
    ├──[➖] enum (53256:11)❌ 
    ├──[➖] enum (53245:11)❌ 
    ├──[➖] enum (53247:11)❌ 
    ├──[➖] enum (53252:11)❌ 
    ├──[➖] enum (53254:11)❌ 
    ├──[➖] enum (53242:11)❌ 
    ├──[➖] enum (53243:11)❌ 
    ├──[➖] enum (53244:11)❌ 
    ├──[➖] enum (53249:11)❌ 
    ├──[➖] enum (53240:11)❌ 
    ├──[➖] enum (53241:11)❌ 
    ├──[➖] enum (53255:11)❌ 
    ├──[➖] enum (53246:11)❌ 
    └──[➖] enum (53248:11)❌ 

Document Element	Total Changes	Breaking Changes
paths	2	2
components	27	17

• ❌ BREAKING Changes: 19 out of 29
• Removals: 17
• Additions: 12
• Breaking Removals: 17
• Breaking Additions: 2

Report

The full API changes report is available at: https:/opensearch-project/opensearch-api-specification/actions/runs/11254952792/artifacts/2034754201

API Coverage

	Before	After	Δ
Covered (%)	588 (57.59 %)	588 (57.59 %)	0 (0 %)
Uncovered (%)	433 (42.41 %)	433 (42.41 %)	0 (0 %)
Unknown	29	29	0

[github-actions]

Spec Test Coverage Analysis

Total	Tested
504	310 (61.51 %)

[dblock]

@Xtansia care to take a look pls?