fix(instrumentation-hapi): fix this binding for plugin register method

[seemk]

Which problem is this PR solving?

#2624

Short description of the changes

Correctly bind this to plugin's register method.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.78%. Comparing base (3bab134) to head (be1b587).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2625   +/-   ##
=======================================
  Coverage   90.78%   90.78%           
=======================================
  Files         169      169           
  Lines        8055     8056    +1     
  Branches     1643     1643           
=======================================
+ Hits         7313     7314    +1     
  Misses        742      742           

Files with missing lines	Coverage Δ
...emetry-instrumentation-hapi/src/instrumentation.ts	99.31% <100.00%> (+<0.01%)	⬆️

[pichlermarc]

thanks 👍