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-45: Update copyright information:

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

GC-37: Implement renewals with new private keys for ECDSA when previous certificate was issued using CSR:

- Added functional test that covers the scenario.
- Parametrise the unit test used to verify that new key generation
follows the same key specification.
- Update test for checking if new private key gets generated to use
key specification instead of key size.

GC-37: Added functional tests for using ECDSA CSRs:

Tests are passing out-of-the box, no changes were required for the
ones added.

GC-27: Fix flake8 linting warnings:

- Properly mark the regex strings as such.

GC-22: Updated renew command to allow reading of CSR from stdin:

- Implemented functional test covering reading of CSR from stdin for
the renew command.
- Updated renew command CLI help.
- Updated renew command to read CSR from stdin if passed-in path is
set to '-'.
- Implemented relevant unit tests.

GC-22: Updated client command to allow reading of CSR from stdin:

- Implemented functional test covering reading of CSR from stdin for
the client command.
- Updated client command CLI help.
- Updated client command to read CSR from stdin if passed-in path is
set to '-'.
- Implemented relevant unit tests.

GC-22: Updated server command to allow reading of CSR from stdin:

- Implemented an additional helper for functional tests for running
interactive commands.
- Implemented functional test covering passing-in CSR to the server
command via stdin (interactively).
- Updated server command implementation.
- Implemented utility function for reading input from user.
- Implemented utility function for reading CSR from string in (in
OpenSSL-style PEM format)
- Fixed some missing imports in the custom pytest fixture.
- Implemented relevant unit tests.

GC-22: Updated renew command to replace existing private key with CSR if passed-in:

- Added functional test which covers renewal of server and client
certificates by generating new private key when previous certificate
was issued using custom CSR.
- Replace the CSR with generate private key when renewing certificate
in case where previous certificate was issued with CSR.
- Added unit tests covering new functionality.

GC-22: Updated renew command to replace existing private key with CSR if passed-in:

- Added functional test which covers renewal of server and client
certificates using CSR when previous certificate was issued using
private key.
- Replaced the private key with CSR when renewing certificate using
CSR in case where previous certificate was issued with private key.
- Updated signature for renew command to accept path to custom CSR.
- Updated existing unit tests for new renew command signature.
- Added unit tests covering new functionality.

GC-22: Updated renew command to report correct artefact if CSR was originally used for issuing certificate:

- Added functional test for covering the scenario.
- Updated printout from the command to display path to CSR if CSR
artefact was used for initial (previous) certificate issuance.
- Updated existing unit tests and implemented new ones.

GC-22: Implemented issuance of server certificates using passed-in CSR:

- Added functional test.
- Expanded server command to accept path to custom CSR file and handle
it appropriatelly.
- Updated existing unit tests to fix command server invocation.
- Added new unit tests.

GC-22: Implemented issuance of client certificates using passed-in CSR:

- Added functional test covering the issuance of client certificate
using CSR.
- Updated default value for the CSR client command option to be
explicitly None.
- Updated the client command to take in the CSR as an argument and
process it accordingly.
- Added helpers for generating CSR, as well as writing and reading
them to/from file.
- Updated existing tests to use new signature for the client
command.
- Added new unit tests for implemented 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.