[msal-v5] Update public docs

[hectormmg]

This pull request updates the documentation for the Microsoft Authentication Library for JavaScript (README.md and lib/msal-browser/README.md) to reflect recent changes in Microsoft branding, clarify package support status, and improve guidance for installation and migration. The most significant changes are the renaming of Azure AD to Microsoft Entra ID, expanded details on package version support and deprecation, and updates to installation and migration instructions.

Branding and terminology updates:

• Replaced references to "Azure AD" with "Microsoft Entra ID" throughout the documentation to reflect Microsoft's updated identity branding. [1] [2]

Package support and versioning:

• Added a detailed "Library Version Support Status" table to clarify current, LTS, and critical security support for each package, and deprecated old CDN usage.
• Updated installation instructions to highlight CDN deprecation and recommend using npm or yarn for package management.

Migration and usage guidance:

• Expanded migration section to include guides for upgrading between major versions (v1.x → v2.x, v2.x → v3.x, v3.x → v4.x, v4.x → v5.x).
• Updated framework wrapper references and removed outdated roadmap and sample links. [1] [2]

Authentication flow documentation:

• Rewrote the section on authentication flows to focus on Authorization Code Flow with PKCE, removing deprecated Implicit Flow details and clarifying migration considerations. [1] [2]