Ecdh import export

[Dringho]

Issue #, if available:

Description of changes:
Script that imports/exports plaintext keys to/from APC using ECDH to generate a AES-256 KEK to wrap a TR-31 block. The script can import/export: AES-256 keys, 3DES_3KEY, 3DES_2KEY.

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[amitkhanal]

@Dringho I'm getting this error as we discussed. Can you please look into it.

`ecdh-tr31-import-export => python3 main.py
Starting AWS Payment Cryptography and Local CA Integration
[?] Select operation mode:

Import a key from a raw plaintext key into AWS Payment Cryptography
Create a random key in AWS Payment Cryptography and export it to plaintext

Selected operation: IMPORT
[?] Select key type:

AES-256 (32 bytes / 256 bits)
Triple DES 2-Key (16 bytes / 128 bits)
Triple DES 3-Key (24 bytes / 192 bits)

Selected key type: AES_256
[?] Select key import method:

Generate a random key
Enter a custom hexadecimal key

Selected import method: random
Will generate a random AES-256 key during execution

=== Starting Execution ===

--- Step 1: Create Local CA and import public CA key ---
Creating local CA
Traceback (most recent call last):
File "/Users/akhnal/Documents/workspace/samples-for-payment-cryptography-service/key-import-export/ecdh-tr31-import-export/main.py", line 460, in
main()
File "/Users/akhnal/Documents/workspace/samples-for-payment-cryptography-service/key-import-export/ecdh-tr31-import-export/main.py", line 254, in main
ca_id = find_or_create_local_ca()
File "/Users/akhnal/Documents/workspace/samples-for-payment-cryptography-service/key-import-export/ecdh-tr31-import-export/crypto_utils.py", line 367, in find_or_create_local_ca
return create_local_ca()
File "/Users/akhnal/Documents/workspace/samples-for-payment-cryptography-service/key-import-export/ecdh-tr31-import-export/crypto_utils.py", line 293, in create_local_ca
now = datetime.datetime.now(datetime.UTC)
AttributeError: module 'datetime' has no attribute 'UTC'`

[Dringho]

@amitkhanal fixed 3.8 retrocompatibility, there was a change in datetime in 3.11 that was breaking previous versions. I tested it with 3.8, 3.11 and 3.13 and it works now, thanks 4 the feedback!