Manifest-tool

- Add support for an external signing tool
- The feature enables to use of an external signing tool for signing the manifest.
- Add a new CLI option `--signing-tool` to the `manifest-dev-tool init` command.
- The `--key` CLI option of the `manifest-dev-tool init` command can receive an identifier private key
or a private key file name that will be used to sign the manifest with the external signing tool provided.
- Add a new configuration option `signing-tool` that is used by the `manifest-tool create` command.
- The `--key` CLI option of the `manifest-tool create` or `manifest-tool create-v1` command can receive
an identifier private key or a private key file name that will be used to sign the manifest with
the external signing tool provided.
- Update `requests` to `2.31.0`.
- Update `cryptography` to `41.0.4`.
- Add support for Python 3.11 (super inits, imports with try, `tox` additions etc.).
- Update `dev-requirements`:
- Update `pytest` to the latest `7.4.2`.
- Update `pylint` to `2.17.7` (`3.0.2` does not support older versions of Python).
- Remove the `--force` CLI option that was deprecated already.

- Fix the minimal required Python version to 3.7.

- Izuma branding, contact email/author updated, Cloud documentation links updated.
- Timeouts for `requests.put/post/delete` operations.
- Pinned down critical Python module versions in `dev-requirements.txt`.
- Module name fixes for some tests.
- Removed obsolete options from `.pylintrc`.
- Support for / testing on Python 3.6 dropped.
- Support for / testing on Python 3.10 added.

- Aarch64 support.

- Add `manifest-package-tool`:
- New tool to generate combined package files for combined updates.
- Update the `README.md` file.

- Add encrypted payload support to `manifest-tool`:
- Add `encrypted-raw` payload format and encrypted payload information to manifest configuration file.
- Add encrypted payload support to `manifest-dev-tool`:
- Add `--encrypted-digest` and `--encrypted-size` options to `create` command.
- Add `--encrypt-payload` option to `update`.
- Build wheels for `manylinux_2_24_x86_64`.
- Improve the tool help and the `README.md` file.