Add support for Flask 3.0.0

[tammy-baylis-swi]

Describe your environment

• Python 3.11
• Otel Python API/SDK 1.20.0
• opentelemetry-instrument 0.41b0
• Flask 3.0.0, released 2 days ago: https://github.com/pallets/flask/releases/tag/3.0.0
• Running on local in docker container FROM python:3.11

Attempting to do opentelemetry-bootstrap after installing Flask 3 results in a quiet message: instrumentation for package flask<3.0,>=1.0 is available but version flask==3.0.0 is installed. Skipping.

Attempting to manually install opentelemetry-instrumentation-flask gives a different message: DependencyConflict: requested: "flask >= 1.0, < 3.0" but found: "flask 3.0.0"

The Flask app successfully loads and Otel API can be used to manually create spans (tracer.start_as_current_span). But SERVER spans are not created for requests accepted by the Flask app that should be intercepted by instrumentation. Here is an example 1-span trace exported to console with only the INTERNAL type span:

172.26.0.1 - - [02/Oct/2023 22:19:02] "GET /test/ HTTP/1.1" 200 -
{
    "name": "my_test_trace",
    "context": {
        "trace_id": "0x3c881a21a3f4f695ebf19c55be7d36c5",
        "span_id": "0xd58cce9986a06144",
        "trace_state": "[]"
    },
    "kind": "SpanKind.INTERNAL",
    "parent_id": null,
    "start_time": "2023-10-02T22:19:02.966587Z",
    "end_time": "2023-10-02T22:19:02.966610Z",
    "status": {
        "status_code": "UNSET"
    },
    "attributes": {},
    "events": [],
    "links": [],
    "resource": {
        "attributes": {
            "telemetry.sdk.language": "python",
            "telemetry.sdk.name": "opentelemetry",
            "telemetry.sdk.version": "1.20.0",
            "service.name": "unknown_service"
        },
        "schema_url": ""
    }
}

Steps to reproduce
I've posted a repo here with two ways to reproduce: https://github.com/tammy-baylis-swi/otel-flask-three

What is the expected behavior?
There should be no errors at bootstrap or manual install/instrument of Flask, and traces should include SERVER type spans when the Flask app receives a request. I think instrumentation should support Flask 3 at some point.

What is the actual behavior?
There are error messages (see above) and traces do not include SERVER type spans when the Flask app receives a request.

Additional context
I think it's from this version requirement in opentelemetry-instrumentation-flask. Upgrading to Flask 3 from the previous 2.3.3 might be breaking so some testing is needed.

[project.optional-dependencies]
instruments = [
  "flask >= 1.0, < 3.0",
]

[ocelotl]

Yes, we currently don't support Flask >= 3.0.0

[tammy-baylis-swi]

Thanks @ocelotl for Label and Title fix!