DOCS-1761 - Document self-service feature opt-in for all customers

[JV0812]

Purpose of this pull request

This pull request extends the existing MSSP-only "Manage Features" self-service opt-in/opt-out capability to all customers managing their own organization (not just child orgs), per DOCS-1761. It also removes references to sub-feature management, which is not currently supported.

• Adds a new Manage features section to manage-org-settings.md, covering opt-in/opt-out for your own organization.
• Removes the two sub-features references from manage-orgs-for-mssps.md.
• Updates mobot.md's "Opting out" section and the AI/ML FAQ to point to self-service opt-out where available.

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

https://sumologic.atlassian.net/browse/DOCS-1761

[JV0812]

@ndhar-sumo Question on sub-feature management in the Manage Features panel, since it affects both this PR and #6979.

This PR originally removed the two "sub-features" references from manage-orgs-for-mssps.md (and didn't add them to the new self-service section in manage-org-settings.md), on the assumption that sub-feature management isn't currently supported:

• "Some features include sub-features. You can expand a top-level feature to manage its sub-features individually."
• "To manage sub-features, click the feature name to expand it and select the desired sub-features."

But #6979 touches the same section of manage-orgs-for-mssps.md and leaves those lines untouched, so I've restored them here rather than ship a contradiction between the two PRs.

Can you confirm: does the Manage Features panel currently support managing sub-features (expand a feature to toggle sub-features individually), or was that description stale/inaccurate to begin with? Want to get this right before either PR merges.