Refactor flask instrumentator configurations

[frandelgado]

Description

Remove the _excluded_urls, _tracer_provider , _request_hook and _response_hook attributes from the _instrumentedFlask class and instead made them instance variables. Fixes #654

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Run tox tests for the flask instrumentator

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Francisco Delgado (fc5abc6, 043931b)