feat: add cli and platform utils

[dariuszd21]

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Migrate format_timestamp cli util from charmcraft.
Add is_managed_mode and get_hostname platform helpers.

(CRAFT-3739)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.39%. Comparing base (0705676) to head (70eb7d0).
Report is 334 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (0705676) and HEAD (70eb7d0). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (0705676)	HEAD (70eb7d0)
	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #599      +/-   ##
==========================================
- Coverage   99.28%   90.39%   -8.90%     
==========================================
  Files          29       66      +37     
  Lines        1265     3987    +2722     
  Branches      209      454     +245     
==========================================
+ Hits         1256     3604    +2348     
- Misses          6      295     +289     
- Partials        3       88      +85     

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[tigarmo]

thanks!

[lengau]

LGTM, thanks!