[INLONG-9876][Manager] optimize the format of error message

[aloyszhang]

• Fixes #9876

Motivation

optimize the format of error message

Modifications

optimize the format of error message. With this pul request, the error msg will be Request to Inlong failed: Inlong group already exists instead of Request to Inlong Inlong group already exists failed: null

Verifying this change

(Please pick either of the following options)

• [x] This change is a trivial rework/code cleanup without any test coverage.

Documentation

• Does this pull request introduce a new feature? (no)