chore: Attached specs to the Shim.prototype for use in custom instrumentation and instrumentation outside of the agent

[bizob2828]

Description

We need to attach the specs to shim if we are going to require customers and ourselves in external repos to instantiante specs at the instrumentation source. This PR assigns specs to Shim.prototype. They then can be access in instrumentation hooks as such:

module.exports = function initialize(shim, Koa) {
  const spec = new shim.specs.MiddlewareSpec({
    req,
    res,
    route: '/foo'
  })

Related Issues

Closes #2036

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.15%. Comparing base (ead8c25) to head (6fcb5e5).
Report is 1 commits behind head on main.

❗ Current head 6fcb5e5 differs from pull request most recent head 414f788. Consider uploading reports for the commit 414f788 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2038   +/-   ##
=======================================
  Coverage   97.15%   97.15%           
=======================================
  Files         247      247           
  Lines       41494    41495    +1     
=======================================
+ Hits        40312    40313    +1     
  Misses       1182     1182           

Flag	Coverage Δ
integration-tests-16.x	78.72% <100.00%> (+<0.01%)	⬆️
integration-tests-18.x	78.70% <100.00%> (+<0.01%)	⬆️
integration-tests-20.x	78.69% <100.00%> (-0.01%)	⬇️
unit-tests-16.x	91.04% <100.00%> (+<0.01%)	⬆️
unit-tests-18.x	91.02% <100.00%> (+<0.01%)	⬆️
unit-tests-20.x	91.02% <100.00%> (+<0.01%)	⬆️
versioned-tests-16.x	75.10% <100.00%> (-0.03%)	⬇️
versioned-tests-18.x	75.32% <100.00%> (-0.03%)	⬇️
versioned-tests-20.x	75.32% <100.00%> (-0.03%)	⬇️

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[jsumners-nr]

Looks good to me.