Make the "lang" URL query optional

[lslezak]

Problem

• Agama fails starting locally on non-UEFI systems

Details

• The lang URL parameter is used only in UEFI systems, on other systems it is not defined/used.
• It is related to feat(i18n): In local installation by default use the EFI locale #1924

Solution

• Make the lang URL query parameter optional

Testing

• Tested manually in bot UEFI and non-UEFI (standard BIOS) systems

[coveralls]

Pull Request Test Coverage Report for Build 13242191167

Details

• 0 of 3 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 70.992%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
rust/agama-server/src/web/http.rs	0	3	0.0%

Totals
Change from base Build 13223989973:	-0.003%
Covered Lines:	17442
Relevant Lines:	24569

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💛 - Coveralls

[bittin]

This is fixed now, thanks for taking care of it