OTRS - raise max-age for STS to 1 year

after we deliberately started with just 7 days
to be careful, now raise it to a year.

this will then also fix the TOO SHORT warning
reported by Qualys SSL Server Test

Strict Transport Security (HSTS)
Yes   max-age=604800   TOO SHORT (less than 180 days)

1 year is also used in examples on OWASP and en.wp

Bug: 38516
Change-Id: I79ca8963e932583b04f715abd4cd4b38f49cc9bf
Merge "OTRS - raise max-age for STS to 1 year" into production