Support for type hints on decorators

Is your feature request related to a problem? Please describe.

Usage of decorators such as @newrelic.agent.function_trace prevent mypy from checking types on those functions. Here is mypy documentation describing this issue: https://mypy.readthedocs.io/en/stable/generics.html#declaring-decorators

For example

import newrelic.agent

@newrelic.agent.function_trace()
def func_i_want_to_trace(value: str) -> bool:
    return value == "yes"

func_i_want_to_trace(1)

mypy will not catch this type mismatch

Feature Description

Type all newrelic.agent decorators as described in the mypy doc

Describe Alternatives

Here is a workaround

F = TypeVar("F", bound=Callable[..., Any])

def newrelic_agent_function_trace(func: F) -> F:
    return cast(F, newrelic.agent.function_trace()(func))

@newrelic_agent_function_trace
def func_i_want_to_trace(value: str) -> bool:
    return value == "yes"

Additional context

I am not sure if this is possible if you would like to keep supporting python 2.7

Priority

Nice to Have

Start by reviewing the newrelic.agent decorators and the linked mypy documentation on declaring decorators. Determine how type hints can cover all agent decorators while preserving the stated Python 2.7 support, then verify that the example mismatch is caught by mypy.