doc/upgrade: add more 6 to 7 changes and minor improvements

[norg]

Issue: #5473

Make sure these boxes are signed before submitting your Pull Request -- thank you.

• I have read the contributing guide lines at https://suricata.readthedocs.io/en/latest/devguide/codebase/contributing/contribution-process.html
• I have signed the Open Information Security Foundation contribution agreement at https://suricata.io/about/contribution-agreement/
• [ x I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Link to redmine ticket:

https://redmine.openinfosecfoundation.org/issues/5473

Describe changes:

• add more of the included changes from 6 to 7
• improve some wording

Provide values to any of the below to override the defaults.

To use a pull request use a branch name like pr/N where N is the
pull request number.

Alternatively, SV_BRANCH may also be a link to an
OISF/suricata-verify pull-request.

SV_REPO=
SV_BRANCH=
SU_REPO=
SU_BRANCH=
LIBHTP_REPO=
LIBHTP_BRANCH=

[github-actions]

NOTE: This PR may contain new authors:

Andreas Herz <aherz@oisf.net>

[victorjulien]

Merged in #9224, thanks!