remove extra upgrade details, add missing config

Update 7.5 update guide:

* Remove unnecessary upgrade details (they were completed in 7.4 upgrade and only needed one time)
* Add missing Nginx config details
Fix typo in the README.md for docker

The container name has been previously renamed to "gitlab_app".
Merge pull request #8429 from zertrin/fix-typo-in-docker-readme-1

Fix typo in the README.md for docker
Add missing webhook doc for tag event
Merge pull request #8374 from bbodenmiller/7-5-update-fix

remove extra upgrade details, add missing config
Merge pull request #8410 from tricknotes/add-webhook-doc-for-tag-event

Add missing webhook doc for tag event