check always-on heartbeat config before on-demand

[deepthi]

Description

Change the order in which we check the config for heartbeats.
Tested manually using the local example.

Related Issue(s)

Fixes #17828

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[deepthi]

@shlomi-noach one other thing I was thinking about is the heartbeat_interval. The default for heartbeats is 1s, but you might want to make them more frequent when they are on-demand without affecting the normal frequency. It was probably not a good idea to use the same frequency for both kinds of heartbeats.

[shlomi-noach]

Please see followup discussion in #17828 (comment)