Added factory class for InstantSource bean creation

[bfg]

For motivation and rationale see #11655

[CLAassistant]

All committers have signed the CLA.

[bfg]

Hey @yawkat, I've created a simple draft for this; I have few questions

• did I place factory class in a correct module and package?
• maybe we should consider creating full Clock type in the future so that client code can query timezone as well?

[yawkat]

The location seems reasonable to me. @graemerocher WDYT

I don't think we should expose a full Clock. The server time zone is not something that microservices should touch anyway.

[bfg]

The location seems reasonable to me. @graemerocher WDYT

I don't think we should expose a full Clock. The server time zone is not something that microservices should touch anyway.

just FYI: I've searched the code and java.time.ZoneId is imported in the following classes:

./http-server-netty/src/main/java/io/micronaut/http/server/netty/handler/accesslog/element/DateTimeElement.java
./context/src/main/java/io/micronaut/scheduling/annotation/Scheduled.java
./context/src/main/java/io/micronaut/scheduling/NextFireTime.java
./context/src/main/java/io/micronaut/scheduling/ScheduledExecutorTaskScheduler.java
./context/src/main/java/io/micronaut/runtime/converters/time/TimeConverterRegistrar.java
./core/src/main/java/io/micronaut/core/reflect/ClassUtils.java
./http/src/main/java/io/micronaut/http/MutableHttpHeaders.java
./http/src/main/java/io/micronaut/http/HttpHeaders.java
./http-netty/src/main/java/io/micronaut/http/netty/NettyHttpHeaders.java

... I guess that scheduling package might need zone, because it's using system default. Dunno, we might be able to work with system default.

In addition it's being used in micronaut-data as well; system default zone is being used by default.

./data-r2dbc/src/main/java/io/micronaut/data/r2dbc/mapper/ColumnIndexR2dbcResultReader.java:import java.time.ZoneId;
./data-r2dbc/src/main/java/io/micronaut/data/r2dbc/mapper/ColumnNameR2dbcResultReader.java:import java.time.ZoneId;
./data-runtime/src/main/java/io/micronaut/data/runtime/convert/DataConversionServiceFactory.java:import java.time.ZoneId;
./data-document-model/src/main/java/io/micronaut/data/document/model/query/builder/MongoQueryBuilder.java:import java.time.ZoneId;
./data-document-model/src/main/java/io/micronaut/data/document/model/query/builder/MongoQueryBuilder2.java:import java.time.ZoneId;