#### What type of PR is this?
/kind cleanup
/area core
/milestone 2.7.x
#### What this PR does / why we need it:
Upgrade Spring Boot to 3.1.1. See https://github.com/spring-projects/spring-boot/releases/tag/v3.1.1 for more.
#### Does this PR introduce a user-facing change?
```release-note
升级 Spring Boot 至 3.1.1
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Bump Halo to 2.7.0-SNAPSHOT for next development iteration.
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind improvement
/area core
#### What this PR does / why we need it:
Replace R2DBC MySQL driver to io.asyncer:r2dbc-mysql. See https://github.com/halo-dev/halo/issues/3804 for more.
Please note that there will be an error like below when starting up Halo on MacOS:
```java
2023-05-09T14:24:45.161+08:00 ERROR 4668 --- [ restartedMain] i.n.r.d.DnsServerAddressStreamProviders : Unable to load io.netty.resolver.dns.macos.MacOSDnsServerAddressStreamProvider, fallback to system defaults. This may result in incorrect DNS resolutions on MacOS. Check whether you have a dependency on 'io.netty:netty-resolver-dns-native-macos'. Use DEBUG level to see the full stack: java.lang.UnsatisfiedLinkError: failed to load the required native library
```
After manual test, I haven't found any problems caused by the error. And this only occurs on MacOS when developing.
#### Which issue(s) this PR fixes:
Fixes https://github.com/halo-dev/halo/issues/3804
#### Special notes for your reviewer:
Steps to test:
1. Start up a MySQL server, e.g.:
```bash
docker run -it --rm --name halodb -p 3306:3306 -e MYSQL_ROOT_PASSWORD=openmysql -e MYSQL_DATABASE=halo mysql:8
```
3. Start Halo with mysql profile active
```bash
make -C console dev
./gradlew bootRun --args="--spring.profiles.active=dev,mysql --halo.plugin.runtime-mode=deployment"
```
5. Check the functionality of Halo
#### Does this PR introduce a user-facing change?
```release-note
替换 R2DBC MySQL 驱动为：io.asyncer:r2dbc-mysql
```
#### What type of PR is this?
/kind chore
/area core
#### What this PR does / why we need it:
Upgrade version to 2.6.0-SNAPSHOT for next development iteration.
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
- Bump up version to 2.5.0-SNAPSHOT for next development
- Update README.md
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Update Halo version to 2.4.0-SNAPSHOT for next development.
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Bump Halo version to 2.3.0-SNAPSHOT and update README.md
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind cleanup
/area core
#### What this PR does / why we need it:
Bump version to 2.2.0-SNAPSHOT for next iteration.
#### Does this PR introduce a user-facing change?
```release-note
None
```
#### What type of PR is this?
/kind improvement
/area core
#### What this PR does / why we need it:
Bump halo version to 2.1.0-SNAPSHOT for next release.
#### Which issue(s) this PR fixes:
```release-note
None
```
#### What type of PR is this?
/kind improvement
/area core
#### What this PR does / why we need it:
Bump Halo version in gradle.properties for next release.
#### Does this PR introduce a user-facing change?
```release-note
None
```
John Niang