Make jersey2 and jersey3 templates as similar to each other as possible. As requested by @wing328.

Jersey 3 doesn't work with useJakartaEe=false. And Jersey 2 doesn't work with useJakartaEe=true.
Jersey 2 is hard-wired to the javax namespace. See e.g. the Jersey 2 class ClientConfig - it implements javax.ws.rs.core.Configurable<ClientConfig> and javax.ws.rs.core.Configuration, but nothing from the jakarta namespace. And vice versa for Jersey 3. You can verify the problem by generating something with library=jersey2 and useJakartaEe=true - the output won't compile due to incompatible types.
It's still beneficial to make the Jersey 2 and Jersey 3 templates as similar as possible, for maintainability. I also added a warning when using useJakartaEe=true with Jersey 2.

Now the only remaining differences between Jersey 2 and Jersey 3 are dependency versions:

$ diff -r modules/openapi-generator/src/main/resources/Java/libraries/jersey2 modules/openapi-generator/src/main/resources/Java/libraries/jersey3
diff -r modules/openapi-generator/src/main/resources/Java/libraries/jersey2/build.gradle.mustache modules/openapi-generator/src/main/resources/Java/libraries/jersey3/build.gradle.mustache
107c107
<     jakarta_annotation_version = "1.3.5"
---
>     jakarta_annotation_version = "2.1.0"
111c111
<     jersey_version = "2.35"
---
>     jersey_version = "3.0.4"
diff -r modules/openapi-generator/src/main/resources/Java/libraries/jersey2/build.sbt.mustache modules/openapi-generator/src/main/resources/Java/libraries/jersey3/build.sbt.mustache
14,18c14,18
<       "org.glassfish.jersey.core" % "jersey-client" % "2.35",
<       "org.glassfish.jersey.inject" % "jersey-hk2" % "2.35",
<       "org.glassfish.jersey.media" % "jersey-media-multipart" % "2.35",
<       "org.glassfish.jersey.media" % "jersey-media-json-jackson" % "2.35",
<       "org.glassfish.jersey.connectors" % "jersey-apache-connector" % "2.35",
---
>       "org.glassfish.jersey.core" % "jersey-client" % "3.0.4",
>       "org.glassfish.jersey.inject" % "jersey-hk2" % "3.0.4",
>       "org.glassfish.jersey.media" % "jersey-media-multipart" % "3.0.4",
>       "org.glassfish.jersey.media" % "jersey-media-json-jackson" % "3.0.4",
>       "org.glassfish.jersey.connectors" % "jersey-apache-connector" % "3.0.4",
35c35
<       "jakarta.annotation" % "jakarta.annotation-api" % "1.3.5" % "compile",
---
>       "jakarta.annotation" % "jakarta.annotation-api" % "2.1.0" % "compile",
Only in modules/openapi-generator/src/main/resources/Java/libraries/jersey3: generatedAnnotation.mustache
diff -r modules/openapi-generator/src/main/resources/Java/libraries/jersey2/pom.mustache modules/openapi-generator/src/main/resources/Java/libraries/jersey3/pom.mustache
407c407
<         <jersey-version>2.37</jersey-version>
---
>         <jersey-version>3.1.1</jersey-version>

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• Read the contribution guidelines.
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