chore: refactored `flask` imports with `starlette` related imports

[viniarck]

@jab1982, when you update kytos you'll need this PR just so it works with starlette that has landed upstream, if you haven't updated kytos and the other NApps locally yet then you can still use as it is though (and then once we move this NApp to kytos-ng org we can create a task there).

Summary

• refactored flask imports with starlette related imports
• updated imports with isort since I had to change some imports
• updated settings urls to avoid concatenating additional slashes

Local Tests

• Enabled amlight/telemetry NApp and sent a POST amlight/telemetry/v1/evc/enable request:

❯ echo '{"evc_ids": []}' | http http://localhost:8181/api/amlight/telemetry/v1/evc/enable
HTTP/1.1 200 OK
content-length: 46
content-type: application/json
date: Wed, 10 May 2023 16:55:10 GMT
server: uvicorn

{
    "f36361422f3149": "no proxy ports available."
}

End-to-End Tests

N/A

[viniarck]

I'll go ahead and merge this since it's pre-requisite to unblock the other tasks. I'll deal with git conflicts from https://github.com/kytos-ng/telemetry/issues/12 later.