store: tweak event display

[nicks]

Hello @nicksieger, @milas,

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

3a9664c (2022-01-25 16:07:24 -0500)
store: tweak event display

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• Commits are adequately tested
• Code is easy to understand and conforms to style guides
• Incomplete code is marked with TODOs
• Code is suitably instrumented with logging and metrics

[nicks]

events now print like this:

[event: pod nicks-env] Container image "localhost:45361/ephctrl-dind:tilt-830bc785828eeaf4" already present on machine
[event: pod nicks-env] Container image "localhost:45361/ephctrl-tilt-upper:tilt-fe2da4a8e4a4d718" already present on machine

which seems more consistent with how other stuff is displayed in tilt