chore: update Gradle build documentation

[jjohannes]

Description:

This updates all documentation referring to Gradle and module setup to the current state. The documentation on "Defining modules and dependencies" was moved to https://github.com/hiero-ledger/hiero-gradle-conventions#modules and updated/extended. This PR adds several links to the documentation in that repository that is now the same for other Hiero and Hedera projects.

Related issue(s):

#14255

Notes for reviewer:

I updated the following files so that they are not outdated anymore. Although I think they could use some general revision on the non-Gradle part (for example, integration tests do not exist in this repository at the moment).

• docs/design/modules.md
• docs/design/services/service-modules.md

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00% (target: -1.00%)	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (6682c10)	96670	69445	71.84%
Head commit (339d3d5)	96670 (+0)	69445 (+0)	71.84% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#17408)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.95%. Comparing base (6682c10) to head (339d3d5).
Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main   #17408   +/-   ##
=========================================
  Coverage     67.95%   67.95%           
  Complexity    22341    22341           
=========================================
  Files          2605     2605           
  Lines         96887    96887           
  Branches      10098    10098           
=========================================
  Hits          65836    65836           
  Misses        27290    27290           
  Partials       3761     3761           

[andrewb1269hg]

Looks good to me!

[anthony-swirldslabs]

LGTM. Thank you!