http-api: T5006: add explicit async to retrieve/configure methods for REST

[jestabro]

Change Summary

The REST endpoints 'retrieve' and 'configure' can reveal a segfault under concurrent connections unless methods are defined explicitly as 'async'. Add async modifier to methods.

This affects only Sagitta REST requests; the segfault will occur in the underlying libc, in vyatta-cfg, respectively, libvyosconfig. Equuleus is not affected, nor are GraphQL requests.

Note that the underlying web framework for the http-api, FastAPI, automatically takes care of red/blue function issues, 'usually'; here is a case where we must be explicit.

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/T5006

Component(s) name

Proposed changes

How to test

Thanks to the user who opened the bug report, testing may be done with:

npx autocannon --duration 10 --connections 4 --renderStatusCodes --method POST --form '{"data": {"type":"text", "value": "{\"op\": \"showConfig\", \"path\": []}"}, "key": {"type":"text","value":"qwerty"}}' 'https://host-name/retrieve'

respectively

npx autocannon --duration 10 --connections 4 --renderStatusCodes --method POST --form '{"data": {"type":"text", "value": "{\"op\": \"set\", \"path\": [\"interfaces\", \"ethernet\", \"eth0\", \"description\", \"baz\"]}"}, "key": {"type":"text","value":"qwerty"}}' 'https://host-name/configure'

for suitable 'host-name'.

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