feat(standalone): support revision in API-driven standalone mode like etcd

[AlinsRan]

Description

In standalone mode, APISIX’s Admin API currently requires clients to retrieve the entire configuration on every sync. As configurations grow in size or change more often, this full-sync approach can lead to unnecessary network traffic and increased latency in applying updates. Moreover, frequent resource changes force a full rebuild of the internal radixtree, which significantly degrades lookup performance under heavy churn.

In the scenario of service discovery, the upstream will always update frequently, and we hope to only update the upstream without affecting the usage of other resources.

Control the changes of each resource by adding <resource-type>_conf_version:

{
    "consumer_groups_conf_version": 1000,
    "consumers_conf_version": 1000,
    "global_rules_conf_version": 1000,
    "plugin_configs_conf_version": 1000,
    "plugin_metadata_conf_version": 1000,
    "protos_conf_version": 1000,
    "routes_conf_version": 1000,
    "secrets_conf_version": 1000,
    "services_conf_version": 1000,
    "ssls_conf_version": 1000,
    "upstreams_conf_version": 1000
    "routes": [
        {
            "id": "r1",
            "uri": "/hello",
            "upstream_id": "u1"
        }
    ],
    "upstreams": [
        {
            "id": "u1",
            "nodes": {
                "127.0.0.1:1980": 1,
                "127.0.0.1:1980": 1
            },
            "type": "roundrobin"
        }
    ]
    "services":[]
}

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[nic-6443]

The title of this PR is not quite appropriate, it can be changed to:
support revision in API-driven standalone mode like etcd

[juzhiyuan]

Hi, please also check the checklist items to make the pr clear

[bzp2010]

Agree in principle with the PR and we can merge when you resolve all the issues on the documentation.

[kayx23]

Doc LGTM