add --init-period and --init-timeout flags

[knQzx]

summary

• adds --init-period flag - used for retries until the first successful sync, then switches to normal --period
• adds --init-timeout flag - max time to keep retrying the initial sync before exiting with failure
• both flags are optional and backward compatible - behavior is unchanged if not set

test plan

• unit tests for chooseWaitTime() and isInitTimedOut() helper functions
• verified all existing tests still pass with go test ./...
• build tested with go build ./...

fixes #959

[linux-foundation-easycla]

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• ✅ login: knQzx / name: knQzx (38c837b, 6a3f31b)

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[thockin]

Thanks. The code looks good, but I'd really like e2e tests to cover these (test_e2e.sh)

[thockin]

please keep this section alphabetical -- these should go earlier

[thockin]

Also, please add to README

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[knQzx]

thanks for the feedback, fixed - moved flags to alphabetical order, added readme docs, and added e2e tests for both init-period and init-timeout