Refine exception message of duplicate key

[JohnNiang]

What type of PR is this?

/kind improvement
/area core
/milestone 2.3.x

What this PR does / why we need it:

I create another exception DuplicateNameException to map org.springframework.dao.DuplicateKeyException when creating extensions.

See #3180 for more.

Which issue(s) this PR fixes:

Fixes #3180

Special notes for your reviewer:

1. Try to create an user which name has already exist
2. See the error

Does this PR introduce a user-facing change?

优化名称重复的错误提示

[guqing]

/lgtm

[ruibaby]

/approve

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ruibaby

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[ruibaby]

/cherry-pick release-2.2

[halo-dev-bot]

@ruibaby: #3219 failed to apply on top of branch "release-2.2":

Applying: Refine exception message of duplicate key
Using index info to reconstruct a base tree...
M	src/main/resources/config/i18n/messages.properties
M	src/main/resources/config/i18n/messages_zh.properties
Falling back to patching base and 3-way merge...
Auto-merging src/main/resources/config/i18n/messages_zh.properties
Auto-merging src/main/resources/config/i18n/messages.properties
CONFLICT (content): Merge conflict in src/main/resources/config/i18n/messages.properties
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Refine exception message of duplicate key
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-2.2

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ruibaby]

/cherry-pick release-2.2

[halo-dev-bot]

@ruibaby: new pull request created: #3278

In response to this:

/cherry-pick release-2.2

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.