fix(spring): refactor retry settings to service-level nested property

[emmileaf]

This PR goes together with GoogleCloudPlatform/spring-cloud-gcp#1392 and:

• Refactors the current setup with method-level and individual settings to use a nested Retry object provided through properties at service-level.

  • Previously, configuring per-setting and per-method :

  <prefix>.language-service.annotate-text-retry-delay-multiplier=2
  <prefix>.language-service.annotate-text-max-retry-delay=PT0.9S
  

  • With this PR, settings provided at service-level will be applied to all rpc methods:

  <prefix>.language-service.retry-settings.retry-delay-multiplier=2
  <prefix>.language-service.retry-settings.max-retry-delay=PT0.9S
  

• Adding method-level property configuration for retry settings will be made incrementally in another PR.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
10 Code Smells

100.0% Coverage
0.0% Duplication

[emmileaf]

Closing in favor of #1143, which extends on top of these commits and adds method-level properties configuration.