chore: add more gravsearch metrics

[BalduinLandolt]

Pull Request Checklist

Task Description/Number

This PR does 2 things:

1. it improves the already reported gravsearch metrics (histogram)
2. it adds a different metric (summary) to see if this works better/worse on datadog

Basic Requirements

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• fix: represents bug fixes
• refactor: represents production code refactoring
• feat: represents a new feature
• docs: documentation changes (no production code change)
• chore: maintenance tasks (no production code change)
• test: all about tests: adding, refactoring tests (no production code change)
• other... Please describe:

Does this PR introduce a breaking change?

• Yes
• No
• Maybe (not 100% sure => check with FE)

Does this PR change client-test-data?

• Yes (don't forget to update the JS-LIB team about the change)
• No

[codecov]

Codecov Report

Patch coverage: 44.00% and project coverage change: -67.03 ⚠️

Comparison is base (7af1c27) 85.13% compared to head (d1e31f8) 18.11%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2666       +/-   ##
===========================================
- Coverage   85.13%   18.11%   -67.03%     
===========================================
  Files         277      277               
  Lines       28958    28947       -11     
===========================================
- Hits        24654     5243    -19411     
- Misses       4304    23704    +19400     

Impacted Files	Coverage Δ
...la/org/knora/webapi/routing/v2/SearchRouteV2.scala	0.00% <0.00%> (-84.93%)	⬇️
...a/org/knora/webapi/util/ZScopedJavaIoStreams.scala	86.36% <ø> (+38.21%)	⬆️
...pi/messages/util/rdf/jenaimpl/JenaFormatUtil.scala	43.28% <50.00%> (-38.81%)	⬇️
...e/triplestore/api/TriplestoreServiceInMemory.scala	73.33% <100.00%> (+73.33%)	⬆️

... and 221 files with indirect coverage changes

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