Improve test matrix to include all supported spring versions

[stliu]

Currently Spring Cloud Azure support multi Spring Boot and Spring Cloud versions, but those versions are not actively tested.

we need to figure out how to enable a matrix tests to actively test all support spring versions and Spring Cloud Azure libraries.

Smoke test

Integration test

[saragluna]

Facts:

• Spring projects release monthly.
• Several types of libraries can be released from Spring projects, snapshot, prerelease, and GA.
• We use multiple Spring projects in Spring Cloud Azure: Spring Framework, Spring Boot, Spring Data, Spring Integration, Spring Cloud Stream, etc.

Expectations:

The Spring Cloud Azure dev branch should align with Spring Boot on the current Spring Boot version.

• Spring Cloud Azure's source code dependency version should rely on the return value from https://spring.io/project_metadata/spring-boot with current: true.
• When the current version from https://spring.io/project_metadata/spring-boot changes, we should catch up ASAP.

The Spring Cloud Azure dev branch should maintain a test matrix for dependent Spring projects. -- UT

• Spring Cloud Azure defines their supported Spring Boot versions,
  • The supported versions change along with Spring releases.
  • Such as supported-versions.json, listing 2.5.1 and 2.6.1 for example.
• Spring Cloud Azure tests on each milestone and GA releases of dependent Spring projects.

The Spring Cloud Azure should have integration tests, containing all Spring Cloud Azure libraries, to run against each version. -- IT

• Ideally, we can call Azure Spring Initializr to generate such a sample project and run it, expecting it throws no exceptions.
• If not the ideal case, we can write such a sample project (probably we put it in the SDK repo) and run it against each version.

Ideas

• The Spring Cloud versions, should be parsed from API like curl -G https://start.spring.io/pom.xml -d packaging=war -o pom.xml and retrieved automatically
• The version matrix should be persistent somewhere, such as spring-cloud-azure-tools repo.