make possible to set the NFS mount options

fate#313208
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fixed typo in Pos*t*processISOURL() function name

Conflicts:
	src/modules/SourceDialogs.ycp
added a note to translators
added changes

Conflicts:
	package/yast2-packager.changes
improved logging, check for empty alias

Conflicts:
	src/modules/AddOnProduct.ycp
the alias must be passed in the URL
fixed log messages
fixed comment
moved the alias handling code to AddOnProduct::SetRepoUrlAlias()
added nil checks
added testsuite
added .gitignore

Conflicts:
	.gitignore
doocument the behavior if an alias is already present in the URL
2.23.1