fix(dev-image): add libwww-perl

[Arjen10]

Description

Add libwww-perl to the dependencies when installing Test::Nginx.

solved build dev image error

21.53 -> FAIL Installing the dependencies failed: Module 'LWP::UserAgent' is not installed
21.53 -> FAIL Bailing out the installation for Test-Nginx-0.32.
21.53 11 distributions installed

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[membphis]

LGTM