Get rid of vulnerable Jinja 2.11.3 dependency

[jo47011]

We are using opencensus on an azure webapp. Our company internal security scanner raises a high security risk for Jinja 2.11.3 which is needed by opencensus-ext-flask version 0.7.6. The issue at Jinja is fixed with version 3.x. So either you can upgrade to that version (due to Flask 2.x dependency, see below) or we need to proof somehow that this is not a security concern. Otherwise we may no longer use this package.

  - opencensus-ext-flask [required: Any, installed: 0.7.6]
    - flask [required: >=0.12.3,<2.0.0,!=1.1.3, installed: 1.1.4]
      - Jinja2 [required: >=2.10.1,<3.0, installed: 2.11.2]

See the statement from Jinja below. We are not using any templates but quite a few 3rd party packages in our software use Jinja, so we cannot assure this, can we? You are the only one requiring flask < 2.0.0. If this could be upgraded everything would be fine.

[eddie-scio]

+1 to this -- in general, could we make this work with a newer version of Flask? < 2.0.0 is nearly a year old now.