[kotlin-spring] fix springdoc dependencies

[un1024]

When I generate with "useSwaggerUI": "false", It generates bellow dependency.

implementation("org.springdoc:springdoc-openapi-webmvc-core:2.2.0-M5")

But it is incorrect dependency(this version is not exists.), so I'm getting the following error.

Could not find org.springdoc:springdoc-openapi-webmvc-core:2.2.0-M5.

I fixed it to use version springdoc v2.
ref: https://springdoc.org/#migrating-from-springdoc-v1

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[un1024]

Java Spring Technical Committee

@cachescrubber (2022/02) @welshm (2022/02) @MelleD (2022/02) @atextor (2022/02) @manedev79 (2022/02) @javisst (2022/02) @borsch (2022/02) @banlevente (2022/02) @Zomzog (2022/09) @martin-mfg (2023/08)

thx.

[wing328]

lgtm. thanks for the PR

fyi
@dr4ke616 (2018/08) @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03) @stefankoppier (2022/06)

[wing328]

UPDATE: filed and merged #19620 to update both api & ui to verison 2.6.0

please pull the latest master to give it another try