feat(security): add 'empty' to forbidden fetch destinations

[SachaMorard]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description

This PR adds 'empty' to the list of forbidden fetch destinations in the do_process_payload function. This change prevents the processing of requests that have an empty fetch destination, which could potentially be used for malicious purposes or cause unnecessary processing overhead.

Changes

• Added 'empty' to the list of forbidden fetch destinations in fastly-edgee/src/proxy/compute/mod.rs

Security Impact

This change improves security by preventing potential abuse through empty fetch destinations.

Related Issues

List related issues here

[coveralls]

Pull Request Test Coverage Report for Build 14702624724

Details

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 49.508%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/server/src/proxy/compute/mod.rs	0	1	0.0%

Totals
Change from base Build 14640564889:	0.0%
Covered Lines:	3524
Relevant Lines:	7118

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💛 - Coveralls