Revise push rules page for CTRT purposes

Major revision of the push rules (https://docs.gitlab.com/ee/user/project/repository/push_rules.html) page, now that several major structural problems have been resolved. Moves items around, removes unneeded subheadings, rewrites wording, and eliminates all Vale issues.

• Reading value before: 6.62 (commit e94d8933f7f0d)
• Reading value after: 6.73 (commit 02c30807931b8)

Related issues

• Related to Move push rules page to better spot (!80242 - merged) (where page was moved)
• Related to Push rules: first round of changes (!85818 - merged) (round 1)
• Related to Push rules page: rename crucial subhead, shift ... (!85845 - merged) (round 2)
• Related to Fix help link for push rules (!85848 - merged)
• Related to Q1FY23 KR: Improve findability, organization, a... (technical-writing#531 - closed)
• Related to Another round of CTRT (!86079 - merged)
• Related to Removed extra words from titles (!86088 - merged)