chore(standalone): add monitoring configuration files

[kwannoel]

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What's changed and what's your intention?

As per title. Basically these can be used by standalone mode users to run grafana, prometheus. Documentation on using these can be found here: risingwavelabs/risingwave-docs#2125

These files should not change much (if at all), they are grafana.ini and prometheus.yaml which just set various host addresses.

For dashboard json specifications, we can just let the user manually import them via grafana's interface, just need to import from /grafana.

We can generate these artifacts via risedev down the road, once we integrate single_node into risedev. Tracked here: #16601.

Can't reuse docker artifacts for these, because they use service name as the addresses instead.

Checklist

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Release note

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[kwannoel]

Bump, let's make sure the documentation gets into 1.9

[kwannoel]

cc @fuyufjh @st1page

[fuyufjh]

Thanks!