Append content type to request header

[Lance52259]

What this PR does / why we need it:
Failed to delete Kafka when using DMS delete function

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged):

NONE

Special notes for your reviewer:

Release note:

1. append content type to request header

[coveralls]

Pull Request Test Coverage Report for Build 1266

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 68.244%

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Totals
Change from base Build 1262:	0.0%
Covered Lines:	11667
Relevant Lines:	17096

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💛 - Coveralls