store: add a return value to OnChange, so we can add re-queueing logic

[nicks]

Hello @milas,

Please review the following commits I made in branch nicks/onchange2:

ee5c389 (2021-06-15 13:44:10 -0400)
store: add a return value to OnChange, so we can add re-queueing logic

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[nicks]

I'm not 100% sure we need this, but i think it will give us more peace of mind to be sure that tilt will eventually retry if it hits an apiserver error

[nicks]

also note that there's very little logic in this change, it's mainly updating signatures and making the linter happy