fix: Update nginx nextcloud.conf for status.php and endpoint caches (fixes http headers), remove extrafiles (fixes admin integrity warning), add comments and readme updates

Unifies MRs !34 (closed), !32 (closed), !30 (closed), !29 (closed), !27 (closed), !22 (closed), !20 (closed)

Fixes:

• adapt nextcloud.conf to only not cache stats endoint (leave other dynamically created css|js|... assets, this also fixes http admin error)
• add snippets to reduce repetition of code
• add nginx:nginx permissions to conf.d/ and move it outside of NC working dir to /var/nextcloud/config.d (fixes admin integrity warning)
• add clearifying comments concerning visibility of environment variables (nextcloud.conf)
• add manifest type to mimetypes

Feats:

• add one unified toggle for encryption (normal + groups)
• add toggle for bruteforceprotection setting
• add location for status.php to only allow basic-auth requests (include htpasword file in conf.d/)
• add readme update about mimtype migration, (d)encryption and maintenance mode

E2E Tests:

• the link to the pipline