GC-47: Add support for Python 3.13:

- Simplify the option presence checks in functional tests to avoid
having to deal with differences in output between Python 3.13 and
older versions (similar checks are already in place for things like
key specification anyway). For more details, see this commit:

https://github.com/python/cpython/commit/c4a2e8a2c5188c3288d57b80852e92c83f46f6f3

GC-48: Update the test framework:

- Slight change required for handling differences in how the output
lines are being broken up during testing.

GC-45: Update copyright information:

- Changes to code base were previously done in 2020 as well (based on
git history).

GC-37: Added support for requesting custom RSA key size when renewing:

- Added functional test.
- Added unit tests.
- Updated existing functional test for renew command help to cope with
addition of one more option (output lines from help changed).
- Added new CLI option for passing-in key specification, used in
combination with the --new-private-key option.
- Renew command function now accepts key specification
parameter. Updated existing code and tests accordingly for the new
function signature.
- If key specification is not passed-in and new private key is
requested, key size is extracted from existing artefacts (e.g. it
does not use CA hierarchy's key size).

GC-23: Implemend option for updating DNS names for renew command:

- Added functional test covering the new functionality.
- Implemented ability to accept new DNS names in the renew command.
- Updated existing unit tests for new function signature.
- Added unit tests covering the new functionality.

GC-22: Added options to parser for accepting CSR for issuing/renewing certificates:

- Implemented functional test for verifying option availability.
- Added CSR option to server, client, and renew commands.
- Make the new CSR option and --new-private-key option exclusive with
each other.

GC-18: Added option for generating a new private key during certificate renewal:

- Implemented functional test for the new scenario.
- Fixed incorrect check for client certificate validity in existing
functional test for client certificate renewal.
- Updated documentation to include information about generating a new
private key during certificate renewal.
- Added option of generating a new private key to the renewal command.
- Updated existing code to use new signature for renewal command and
function.
- Added inline function documentation for the renew command code.
- Implemented relevant unti tests that cover new option.

GC-18: Added functional renew command implementation:

- Added functional test covering the use of renew command for server
and client certificates.
- Added new crypto function for renewing a certificate based on
existing certificate, issuer private key, and issuer certificate.
- Fixed use of incorrect output stream in one of the existing tests
for the renew command.
- Added unit tests covering new functionality.

GC-18: Fail the renew command if requested entity has not certificate:

- Added functional test for scenario where renewal is requested for
server or client certificate that do not exist already.
- Updated the renew command to return a new error code and show
appropriate error message.
- Added unit tests.

GC-18: Error-out in case renew is called on uninitialised hierarchy:

- Added functional test for scenario.
- Implemented dummy renew command that for now just verifies the
hierarchy has been initialised.
- Implemented unit tests.

GC-18: Added initial dummy implementation of the renew command:

- Added functional test covering testing of available help for the
renew command.
- Implemented unit tests
- Registered a renew command parser setup function with CLI.