#2156: Add secret placeholders for configuration templates

[Caylipp]

This PR fixes #2156

Implemented changes:

• added generic $[secret:<name>] placeholders for files under templates/conf/
• prompted once per distinct secret name within each template file
• supported repeated and multiple distinct placeholders
• ensured secrets are only written to generated local conf/ files
• preserved source templates and existing local configuration files
• prevented secret values from appearing in production logs
• handled $ and \ in secret values safely

---

Testing instructions

Please add conscise, understandable instructions on how a reviewer can test/verify the functionality of your contribution here:

1. Run the focused tests: mvn -pl cli -Dtest=CreateCommandletTest test
2. Run the complete CLI test suite: mvn -pl cli test
3. Optional: Run the ./build-local-dev.sh script and create a test project

---

Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. #921: fixed setup.bat). If no issue ID exists, title only.
• PR top-level comment summarizes what has been done and contains link to addressed issue(s)
• PR and issue(s) have suitable labels
• Issue is set to In Progress and assigned to you or there is no issue (might happen for very small PRs)
• You followed all coding conventions
• You have added the issue implemented by your PR in CHANGELOG.adoc unless issue is labeled
  with internal
• You have formulated clear instructions on how to test your contribution under "Testing instructions"

[coveralls]

Coverage Report for CI Build 29498958581

Coverage increased (+0.07%) to 72.572%

Details

• Coverage increased (+0.07%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 26 coverage regressions across 2 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

26 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
com/devonfw/tools/ide/commandlet/AbstractUpdateCommandlet.java	25	84.12%
com/devonfw/tools/ide/tool/ide/IdeToolCommandlet.java	1	78.33%

---

Coverage Stats

Relevant Lines:	16815
Covered Lines:	12718
Line Coverage:	75.63%
Relevant Branches:	7500
Covered Branches:	4928
Branch Coverage:	65.71%
Branches in Coverage %:	Yes
Coverage Strength:	3.2 hits per line

---

💛 - Coveralls

[Caylipp]

I noticed that this PR partially overlaps with the broader prompting feature discussed in the related issue #2165. This implementation currently focuses on generic secret placeholders using $[secret:name].