Style guide improvements to Source Code docs

doc/administration/integration/diagrams_net.md

doc/administration/lfs/index.md

doc/administration/operations/fast_ssh_key_lookup.md

doc/administration/settings/account_and_limit_settings.md

doc/administration/settings/instance_template_repository.md

doc/administration/settings/push_event_activities_limit.md

doc/api/commits.md

doc/api/graphql/branch_rules.md

doc/api/protected_branches.md

doc/api/repository_submodules.md

doc/api/tags.md

doc/development/code_owners/index.md

doc/development/developing_with_solargraph.md

doc/development/fe_guide/source_editor.md

doc/development/fips_compliance.md

doc/development/gitlab_shell/features.md

doc/development/gitlab_shell/index.md

doc/development/internal_api/index.md

doc/development/internal_api/internal_api_allowed.md

doc/development/lfs.md