lib-sieve: variables extension: Rename settings to better match Dovecot conventions

src/lib-sieve/plugins/enotify/vmodf-encodeurl.c

src/lib-sieve/plugins/include/ext-include-variables.c

src/lib-sieve/plugins/variables/ext-variables-arguments.c

src/lib-sieve/plugins/variables/ext-variables-common.c

src/lib-sieve/plugins/variables/ext-variables-limits.h

src/lib-sieve/plugins/variables/ext-variables-modifiers.c

src/lib-sieve/plugins/variables/ext-variables-operands.c

src/lib-sieve/plugins/variables/ext-variables-settings.c

src/lib-sieve/plugins/variables/ext-variables-settings.h

src/lib-sieve/plugins/variables/sieve-ext-variables.h

tests/extensions/enotify/encodeurl.svtest