Migration and Update Guide for 5 to 7

[mmattel]

References:
#1028 (Migration and Update Guide for 5 to 7)
#1034 (CLI: health check for services (to be added in maintenance commands)
#1038 (Update the compose examples to be ready to upgrade for the next release)
owncloud/ocis#10439 (Restart Postprocessing Properly) (CLI change)
owncloud/ocis#10499 ([docs-only] Create envvar delta files after v5 to master (v7.0.0))
owncloud/ocis#10566 ([docs-only] Improve error messages for health command output)

Updates the migration, update and envvar changes documentation.

Currently visible on staging

• Added/Removed envvar .adoc table files in ocis/docs/services/general-info/envvar-deltas
• Added/Changed/Removed CLI commands
• Config changes when running ocis init --diff
• Breaking changes
  activitylog: service_account: + value in ocis.yaml (via ocis init --diff)
  collaboration: wopi.secret + value in ocis.yaml (via ocis init --diff)
• Added content that is ocis 7 relevant found during update writing
  (There will be most likely more content that gets added post merging)

IMPORTANT
These changes also require a final docs branching where we reference to versioned ocis content that MUST be provided to make this final. Some things get automatically referenced with branching pointing to the correct ressources included.

[ScharfViktor]

step https://doc.staging.owncloud.com/ocis/next/migration/upgrading_5.0.x_7.0.0.html#update-config-settings for docker doesn't work because patch command is currently missing in the ocis docker image

[mmattel]

for docker doesn't work because patch command is currently missing

A commit has been added with a note what to do if the patch command is missing.
Master/7 has the patch command, rolling not.

[micbar]

Approving. Overall, everything is fine. Small tweaks can be made later in subsequent PRs.