feat(fastify): Skip update HTTP's span name and update RpcMetadata's route instead

[chigia001]

Which problem is this PR solving?

Each framework has a different approach to updating Span's name and HTTP_ROUTE attribute. We want to delegate this to instrumentation-http for consistent's name and attribute
This PR fixes the above issue for fastify

• This will partially fix issue Setting HTTP_ROUTE inconsistent accross HTTP server frameworks #1381

Short description of the changes

• Skip modifying HTTP's Span name directly in instrumentation-fastify code
• Update route property of RpcMetadata
• As instrumentation-fastify's unit test already integrate with instrumentation-http, there are no need to update any test

[codecov]

Codecov Report

Merging #1569 (73c7033) into main (bf25eb1) will decrease coverage by 0.72%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1569      +/-   ##
==========================================
- Coverage   96.06%   95.35%   -0.72%     
==========================================
  Files          14       20       +6     
  Lines         914     1183     +269     
  Branches      199      246      +47     
==========================================
+ Hits          878     1128     +250     
- Misses         36       55      +19     

Impacted Files	Coverage Δ
...try-instrumentation-fastify/src/instrumentation.ts	97.60% <100.00%> (ø)

... and 5 files with indirect coverage changes