Add tzdata package for timezones

[Jancis]

This allows setting timezone via TZ environment variable but will require chart change.

php:
  env:
    TZ: Europe/Helsinki

Alternative option is pre-setting tz via /etc/localtime and /etc/timezone, but overriding won't be as straightforward.

RUN apk add tzdata
ENV TZ=Europe/Helsinki
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone