feat: Add OpenAPIConnector component, improve OpenAPI integration

[vblagoje]

Why:

Enables invocation of REST endpoints specified in an OpenAPI specification.

What:

• Introduced OpenAPIConnector, a new component to invoke REST endpoints from OpenAPI specs.
• Updated __init__.py to include OpenAPIConnector in the exports.
• Added comprehensive unit and integration tests for OpenAPIConnector to ensure its correctness and reliability.

How can it be used:

The OpenAPIConnector can be used to perform API operations defined in an OpenAPI specification. Initialize it with an OpenAPI spec URL, file path, or string, and use it to call endpoints:

from haystack.utils import Secret
from haystack.components.connectors.openapi import OpenAPIConnector

connector = OpenAPIConnector(
    openapi_spec="https://bit.ly/serperdev_openapi",
    credentials=Secret.from_env_var("SERPERDEV_API_KEY")
)
response = connector.run(
    operation_id="search",
    parameters={"q": "Who was Nikola Tesla?"}
)

How did you test it:

Tests cover initialization, serialization, deserialization, and execution of operations to ensure component functionality.

Notes for the reviewer:

• The test_openapi_connector.py file contains both unit and integration tests; some tests require environment variables like SERPERDEV_API_KEY or GITHUB_TOKEN to run integration tests, which are conditionally skipped if not present.
• Pay special attention to the integration with openapi-llm and the potential requirements for the environment setup.

[coveralls]

Pull Request Test Coverage Report for Build 13138425556

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 91.322%

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Totals
Change from base Build 13137152845:	0.02%
Covered Lines:	8977
Relevant Lines:	9830

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💛 - Coveralls