docs: update links for v2

[bmorelli25]

Fixes changed links in new APM Server documentation.

Only merge after elastic/apm-server#1530

[codecov-io]

Codecov Report

Merging #297 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #297      +/-   ##
============================================
+ Coverage     72.31%   72.38%   +0.06%     
  Complexity     1180     1180              
============================================
  Files           131      131              
  Lines          4458     4458              
  Branches        451      451              
============================================
+ Hits           3224     3227       +3     
+ Misses         1026     1023       -3     
  Partials        208      208

Impacted Files	Coverage Δ	Complexity Δ
.../main/java/co/elastic/apm/bci/ElasticApmAgent.java	71.75% <0%> (+2.29%)	19% <0%> (ø)	⬇️

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