Should have vary header with auto heif and avif

[devppjr]

This PR aims to add Vary header in Thumbor response to avoid problems with downstream caches.

Closes https://github.com/thumbor/thumbor/issues/1563 thanks @mpdude

[coveralls]

Pull Request Test Coverage Report for Build 7085966994

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.687%

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Totals
Change from base Build 7066104908:	0.0%
Covered Lines:	4011
Relevant Lines:	4627

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💛 - Coveralls

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[mpdude]

Thank you!