[19.0][OU-ADD] website_*: noupdate handling

[dnplkndll]

Pre-migration scripts for 4 website_* modules + noupdate_changes.xml decision for 1 (website_event). Split from #5633 to separate the substantial migration code from the 26 trivial annotations (now #5633a).

Pre-migration scripts (noupdate record deletion via direct SQL):

• website_crm_partner_assign — deletes 2 website_membership noupdate ir.rules.
• website_event_sale — deletes event_product_template_public noupdate ir.rule.
• website_livechat — deletes im_livechat_channel_rule_public noupdate ir.rule.
• website_slides — deletes mail_activity_data_access_request noupdate mail.activity.type.

noupdate_changes.xml decisions:

• website_event — 2 ir.rule domain_force updates left active (security framework migration).
• website_slides — mail_notification_channel_invite template removed from file (preserves operator-customized template body; outer <!-- --> wrapping would have produced invalid XML due to nested HTML comments).

docsource: all 5 modules marked Done to opt into CI migration tests.

[dnplkndll]

@MiquelRForgeFlow @pedrobaeza @remi-filament

ready for review. Pair with #5663 (the trivial-annotation sibling). Together they replace the closed
#5633 (split per [MIG] vs [OU-ADD] convention)