This pull request adds support for updating multiple file system types via OTA (Over-The-Air) updates, refactors the update logic to generalize file system handling, and introduces new update methods for various file systems. The changes improve flexibility and maintainability by replacing the previous SPIFFS-only logic with support for SPIFFS, FATFS, LittleFS, and a generic file system mode. Additionally, several code cleanups and refactorings are included.

File System OTA Update Support:

• Added new constants (U_FLASHFS,U_FATFS,U_LITTLEFS) toUpdate.h to represent different file system OTA update modes, and refactored code to use these instead of onlyU_SPIFFS.
• Updated theUpdateClass::begin method and OTA partition selection logic to support SPIFFS, FATFS, LittleFS, and a generic file system mode (U_FLASHFS), including fallback logic for partition selection.
• Refactored thehandleUpdate method inHTTPUpdate.cpp to accept a file system type parameter instead of a boolean, and to set appropriate HTTP headers and select the correct partition for each file system type.[1][2][3][4][5]

API Additions and Refactoring:

• Added new update methods for file systems (updateFs,updateFatfs,updateLittlefs) to bothHTTPUpdate.h andHTTPUpdate.cpp, for bothNetworkClient andHTTPClient usage.[1][2]
• Updated function signatures and internal logic to use the new file system type constants, replacing previous boolean flags and simplifying the API.[1][2]

Code Cleanup and Documentation:

• Removed the unused_paroffset member fromUpdateClass and related logic, simplifying partition offset handling.[1][2]
• Updated documentation and comments to clarify that OTA file system updates now support multiple types, not just SPIFFS.[1][2]
• Updated example code and server logic to use the new generic file system mode (U_FLASHFS) instead of SPIFFS.[1][2]

Backward Compatibility and Generalization:

• Generalized header verification and completion logic inUpdater.cpp to work for all file system types, not just SPIFFS.[1][2]
• Updated OTA command parsing and handling to support the new file system modes, ensuring correct update behavior for all supported types.

These changes collectively make the OTA update process more robust and extensible for different file system types on ESP32 platforms.

Fixes:#9347