docs/develop: Replace g_dbus_proxy_call with g_dbus_connection_call

[johan-bjareholt]

Describe your changes

The example in "VAPIX access for ACAP applications" creates a connection to the bus, creates a proxy object and then calls the method. Creating a proxy for this use-case is unnecessary and does one or more D-Bus calls under the hood as you do not pass G_DBUS_PROXY_FLAGS_DO_NOT_LOAD_PROPERTIES which is necessary to make this request "lightweight". The better solution is to skip the proxy completely and just use g_dbus_connection_call_sync, as we do not use any of the features of the proxy.

Issue ticket number and link

N/A

Checklist before requesting a review

• I have performed a self-review of my own code
• I have verified that the code builds perfectly fine on my local system
• I have added tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have verified that my code follows the style already available in the repository
• I have made corresponding changes to the documentation

[pataxis]

Hi @johan-bjareholt , thank you for your contribution, much appreciated, it was integrated in #107 !

FYI, this PR was closed due to the one-directional sync procedure we currently have between a staging repo and this public repo.
We want to change the flow to something that works better for public contributions like this in a not to far future.