feat(instrumentation-koa): identify middleware functions inside route handlers

[satazor]

Which problem is this PR solving?

Considering the following route handler:

const someMiddleware = () => async function some(ctx, next) => {
  await next();
});

router.get('/post/:id', someMiddleware(), (ctx) => {
  ctx.body = `Post id: ${ctx.params.id}`;
});

...will generate two spans with the same name: router - /post/:id, even though the first handler is actually a named middleware (some).

Ideally, it would generate two different spans:

• middleware - some
• router - /post/:id

Short description of the changes

The changes are quite simple: when iterating these handlers, we assume they are a middleware if it's not the last handler on the stack and if it has a name.

[satazor]

cc @dyladan

Not sure who can look into this since it seems there's no maintainer for this package.

[codecov]

Codecov Report

Merging #2037 (a4cba8d) into main (dfb2dff) will increase coverage by 0.00%.
Report is 15 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2037   +/-   ##
=======================================
  Coverage   90.97%   90.98%           
=======================================
  Files         146      145    -1     
  Lines        7492     7455   -37     
  Branches     1502     1489   -13     
=======================================
- Hits         6816     6783   -33     
+ Misses        676      672    -4     

Files	Coverage Δ
...lemetry-instrumentation-koa/src/instrumentation.ts	95.45% <100.00%> (+0.05%)	⬆️

... and 5 files with indirect coverage changes

[satazor]

Shamelessly pinging @pichlermarc and @trentm 😅

[satazor]

cc @blumamir

[satazor]

Bump :/