T5786: Add set/show system image to /image endpoint

[HollyGurza]

Change Summary

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T5786

Related PR(s)

Component(s) name

Proposed changes

How to test

curl --location 'https://vyos_url/image' \
--header 'Content-Type: application/json' \
--data '{
    "key": "api_key",
    "op": "show"
}'

curl --location 'https://vyos_url/image' \
--header 'Content-Type: application/json' \
--data '{
    "key": "api_key",
    "op": "set_default",
    "name": "1.5-rolling-20240527002"
}'

Smoketest result

vyos@vyos:~$ python3 /usr/libexec/vyos/tests/smoke/cli/test_service_https.py 
test_api_add_delete (__main__.TestHTTPSService.test_api_add_delete) ... ok
test_api_auth (__main__.TestHTTPSService.test_api_auth) ... ok
test_api_config_file (__main__.TestHTTPSService.test_api_config_file) ... ok
test_api_config_file_load_http (__main__.TestHTTPSService.test_api_config_file_load_http) ... ok
test_api_configure (__main__.TestHTTPSService.test_api_configure) ... ok
test_api_generate (__main__.TestHTTPSService.test_api_generate) ... ok
test_api_image (__main__.TestHTTPSService.test_api_image) ... ok
test_api_incomplete_key (__main__.TestHTTPSService.test_api_incomplete_key) ... ok
test_api_missing_keys (__main__.TestHTTPSService.test_api_missing_keys) ... ok
test_api_reset (__main__.TestHTTPSService.test_api_reset) ... ok
test_api_show (__main__.TestHTTPSService.test_api_show) ... ok
test_certificate (__main__.TestHTTPSService.test_certificate) ... ok

----------------------------------------------------------------------
Ran 12 tests in 98.410s

OK

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly