AG-43745 Add urltransform supported version for browser-extension

[techi9]

Update $urltransform modifier documentation to reflect new platform support:

• Mark $urltransform as supported in AdGuard Browser Extension (v5.5+) and AdGuard for Chrome MV3 in the compatibility table
• Add MV3 limitations section ($urltransform modifier limitations) covering: no decode stages, no global replacement, single redirect per request
• Update "Changing the origin" compatibility note to include Browser Extension v5.5+

[github-actions]

Preview was deployed to: https://pull-request-875.kb-adg.pages.dev/

[techi9]

Merge when v5.5 released