Correct invalid monitor ID encoding

[rmfitzpatrick]

#266 introduced a regression where monitor ids with unsupported characters are not used as monitorID dimension values, causing the collectd write server to drop points. Instead of url encoding these changes strip all non-word characters.

[codecov]

Codecov Report

Merging #269 (08a5ab2) into main (c213260) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #269   +/-   ##
=======================================
  Coverage   86.93%   86.93%           
=======================================
  Files          20       20           
  Lines        1492     1492           
=======================================
  Hits         1297     1297           
  Misses        160      160           
  Partials       35       35           

Impacted Files	Coverage Δ
internal/receiver/smartagentreceiver/receiver.go	91.89% <100.00%> (ø)

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