fix: using connection manager shared

[pablocarle]

Description

#4383 fixed an issue with CLOSE_WAIT state connections but introduced a problem with evictor threads.
Each time the Eureka server requires a new connection (upon errors for example) it creates a new http client with its own eviction thread. These accumulate over time eventually leading to exhaust the z/OS thread limit.

Type of change

• fix: Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• PR title conforms to commit message guideline ## Commit Message Structure Guideline
• I have commented my code, particularly in hard-to-understand areas. In JS I did provide JSDoc
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The java tests in the area I was working on leverage @nested annotations
• Any dependent changes have been merged and published in downstream modules

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud