feat: enable root span route instrumentation without any express layer spans

[shyimo]

Which problem is this PR solving?

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In addition to #176 PR, We should able to instrument the root span name when ignoring all express layers (router, middleware and request_handler).
This significantly reduces the amount of spans for a large and complex express based micro-service with large amount of outgoing http requests for a single incoming http request and still able to set the route on the root span.

Short description of the changes

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using express with only request_handler layer before the change:

using express without request_handler, middleware and route layer (root span name not modified) before the change:

using express without request_handler, middleware and route layer after the change:

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Shai Moria (8fe3977)

[codecov]

Codecov Report

Merging #273 (5c2dc21) into master (130985b) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #273      +/-   ##
==========================================
+ Coverage   95.32%   95.35%   +0.03%     
==========================================
  Files         115      115              
  Lines        5948     5991      +43     
  Branches      586      591       +5     
==========================================
+ Hits         5670     5713      +43     
  Misses        278      278              

Impacted Files	Coverage Δ
node/opentelemetry-plugin-express/src/express.ts	97.19% <0.00%> (+0.05%)	⬆️
.../opentelemetry-plugin-express/test/express.test.ts	99.44% <0.00%> (+0.16%)	⬆️

[dyladan]

This is a very different behavior but it doesn't look like you added any configuration options. Am I missing something?

[shyimo]

Hi @dyladan.
Thats true, i didn't add any new configuration to the plugin.
The change only verify that we will modify the root span name with the current request path (for example: HTTP POST -> POST user/:userid) when not using the request_handler express layer.
currently, the root span name is modified only when request_handler layer is on and this adds many tiny spans that sometimes is not needed

[shyimo]

@obecny Hi. i fix your comments on the unit test structure

[obecny]

lgtm, thx for those changes