[FLINK-14100][jdbc] Added Oracle dialect

[fpompermaier]

What is the purpose of the change

Add the implementation of the Oracle dialect for JDBC connectors

Brief change log

• Implemented OracleDialect extending AbstractDialect in JDBCDIalects
• Added default OracleRowConverter
• Added getMergeIntoStatement() into JDBCDialect to handle upsert

Verifying this change

I tested this change connecting directly to a running database (but I didn't cover all the types).

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? docs

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Automated Checks

Last check on commit 8ab267b (Fri May 28 08:16:10 UTC 2021)

Warnings:

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• 8ab267b Azure: FAILURE

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[eskabetxe]

@fpompermaier could you solve the conflicts..
@wuchong could you check this

[cmdares]

https://ci.apache.org/projects/flink/flink-docs-release-1.12/zh/dev/table/connectors/jdbc.html

Database	Upsert Grammar
MySQL	INSERT .. ON DUPLICATE KEY UPDATE ..
PostgreSQL	INSERT .. ON CONFLICT .. DO UPDATE SET ..
**Oracle	Merge into
merge into [target-table] A using [source-table sql] B on ([conditional expression] and [...]...)
when matched then [update sql]
when not matched then [insert sql]**

[qinjunjerry]

@fpompermaier anything pending before the conflicts can be solved and the PR to be merged?

[eskabetxe]

I resolved the conflicts and update to new changes introduced in https://issues.apache.org/jira/browse/FLINK-24253 here #17676

[MartijnVisser]

@eskabetxe I misread your comment, thanks for the PR! I'll try to find a reviewer for that.

[leonardBang]

Thanks @fpompermaier and @eskabetxe for the contribution to support Oracle Database, I close this PR now.