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

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9b41ea5) 88.35% compared to head (f09c49e) 88.35%.

:exclamation: Current head f09c49e differs from pull request most recent head d86e248. Consider uploading reports for the commit d86e248 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #674 +/- ## ========================================= Coverage 88.35% 88.35% + Complexity 779 775 -4 ========================================= Files 173 173 Lines 7078 7078 Branches 393 393 ========================================= Hits 6254 6254 Misses 699 699 Partials 125 125 ```

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