docs: Add instructions for using Spring Boot prior to version 2.7

[shengbinxu]

Closes #

Proposed Changes

1. When I introduced the influxdb-spring dependency into my Spring Boot 2.3 project, auto-configuration did not take effect, requiring additional code to be added. As a result, I updated the readme to provide instructions.

2. In the Maven repository influxdb-spring, the dependency for micrometer-registry-influx has already been added. Consequently, developers using influxdb-spring no longer need to manually import the micrometer-registry-influx dependency. Due to package conflicts, the spring-boot-actuator may have relied on an earlier version of the micrometer-core. Therefore, it is necessary to specify a higher version here.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• mvn test completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.35%. Comparing base (9b41ea5) to head (d86e248).
⚠️ Report is 170 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff            @@
##             master     #674   +/-   ##
=========================================
  Coverage     88.35%   88.35%           
+ Complexity      779      777    -2     
=========================================
  Files           173      173           
  Lines          7078     7078           
  Branches        393      393           
=========================================
  Hits           6254     6254           
  Misses          699      699           
  Partials        125      125           

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[bednar]

@shengbinxu thanks for your PR!

LGTM 🚀

Just for your information, PR #673 in the influxdb-client-java repository introduces support for Spring Boot 3. Consequently, the newest version of the client will no longer be compatible with Spring Boot 2.x.