[MASTER] Document Spartacus Security

Need to document security management, concerns, recommendations and best practices in Spartacus.

See the following:

• https://github.com/SAP/cloud-commerce-spartacus-storefront/issues/3615
• https://github.com/SAP/cloud-commerce-spartacus-storefront/issues/3611

Additionally:

1. Document that storing such data in local/Session storage may be dangerous (e.g. multi-page under one URL) or have DPP concerns (per data storage) (ref: https://github.tools.sap/cx-commerce/spasec/issues/2)
   See "Session Management" doc ticket below.

2. Document necessity for encryption in security guide! (as spartacus does not enforce HTTPS, users security can be threatened if operating party deploys it using HTTP) (ref: https://github.tools.sap/cx-commerce/spasec/issues/4)
   See "Authentication in HTTPS" doc ticket below.

3. The use of headers to prevent the load of the UI on an iFrame is required. (https://github.tools.sap/cx-commerce/spasec/issues/11)
   See "Clickjacking" doc ticket below.

Actionable Tickets:

• Session Management: https://github.com/SAP/cloud-commerce-spartacus-storefront-docs/issues/327
• Authentication in HTTPS: https://github.com/SAP/cloud-commerce-spartacus-storefront-docs/issues/328
• Clickjacking: https://github.com/SAP/cloud-commerce-spartacus-storefront-docs/issues/329

Start by reviewing the linked documentation issues 327, 328, and 329, which split this master request into Session Management, Authentication in HTTPS, and Clickjacking. Confirm their current status and scope; the security documentation is complete when those three topics cover the listed storage, encryption, and framing concerns.