* sync: Add experimental flag to configure the self-hosted sync service URL. * sync: Set the |BRAVE_SYNC_ENDPOINT| directly in kSyncServerUrl/kSyncDevServerUrl using chromium_src overrides instead of passing it via command_line * sync: Remove the test case for checking if the BRAVE_SYNC_ENDPOINT is set via the command line. * sync: Improve self-hosted sync URL validation and rename flag - Enhanced validation to accept only valid HTTPS URLs or trustworthy HTTP origins (e.g., localhost) - Renamed sync URL flag to brave-override-sync-server-url and updated its description. * sync: fix build issue due to GN deps * Update text desc in browser/about_flags.cc Co-authored-by: Francois Marier <francois@fmarier.org> * sync: Add tests for Self-host sync server URL validation Add parameterized browser tests to verify the logic in `BraveMainDelegate` for handling the `--sync-url` command-line switch / feature flag. The tests cover the following scenarios: - Secure HTTPS URLs are accepted. - Insecure HTTP URLs are rejected by default. - HTTP URLs for localhost are accepted (as a trustworthy origin). - Insecure HTTP URLs are accepted if the origin is explicitly marked as secure via `--unsafely-treat-insecure-origin-as-secure`. - The absence of the `--sync-url` switch. * sync: add a warning when the user provided sync url is invalid * sync: address test failures likely caused by merge conflicts * test: Filter HistoryNoticeUtilsTest.WebHistoryStates due to sync endpoint change The test fails because it expects Google's sync server endpoint while Brave uses a different sync server endpoint. --------- Co-authored-by: Brian Clifton <brian@clifton.me> Co-authored-by: Francois Marier <francois@fmarier.org>