STORE .... (txt) stores a comma separated file with normal quoting rules (msq). Because the file only contains a single 'field', and this field contains commas and quotes, the field is quoted (double quotes at the start and end), and doubling up internal double quotes to 'escape' them.
You can change the delimiter, but I don't think you can change the quoting rules to no quotes. XML will accept single quotes, so you could try using single quotes like:
LET vXML = '<?xml version=''1.0'' encoding=''utf-8'' ?>' & CHR(10) & '
<configuration>' & CHR(10) & '
<configSections>' & CHR(10) & '
<sectionGroup name=''applicationSettings'' .....
Note that ''1'' is a 1 surrounded with two single quotes on each side to escape the single quote and is less complicated than embedding chr(x) statements.