Support %ARCHISO_UUID% variable in boot loader configuration

This allows to replace archisolabel=%ARCHISO_LABEL% with archisodevice=UUID=%ARCHISO_UUID% in boot loader configurations.

Related to #202 (closed)

changed milestone to %v71

added scopeenhancement label

requested review from @dvzrv

assigned to @nl6720

added 2 commits

• 81853086 - Use UUIDs in all boot loader configuration files
• dcd4561a - mkarchiso: read SOURCE_DATE_EPOCH from file early

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added 5 commits

• 20fc8030 - 1 commit from branch archlinux:master
• db5d6a54 - mkarchiso: support %ARCHISO_UUID% variable in boot loader configuration
• c426bbfc - Use UUIDs in all boot loader configuration files
• 81fbade1 - mkarchiso: read SOURCE_DATE_EPOCH from file early
• 2747f7a7 - README.profile.rst: document %ARCHISO_UUID% and %ARCHISO_SEARCH_FILENAME%

Compare with previous version

added 14 commits

• 2747f7a7...b4683274 - 10 commits from branch archlinux:master
• 094afd16 - mkarchiso: support %ARCHISO_UUID% variable in boot loader configuration
• ce8fdedb - Use UUIDs in all boot loader configuration files
• 8cc0e9e5 - mkarchiso: read SOURCE_DATE_EPOCH from file early
• db292a59 - README.profile.rst: document %ARCHISO_UUID% and %ARCHISO_SEARCH_FILENAME%

Compare with previous version

merged