Configure reactions to errors in the handlers, per-handler

[nolar]

Extra keywords for the handlers to override the default exception-reacting behaviour (timeouts, retries, cool-down periods, arbitrary error interpretations).

Issue : closes #16

Description

With this PR, the error handling mode can be configured by handler (for arbitrary exceptions):

• Treat them as permanent: errors=kopf.ErrorsMode.PERMANENT
• Treat them as temporary for N attempts: retries=3
• Treat them as temporary for some time: timeout=60 (exists already)
• Ignore them -- same as permanent, with better logging: errors=kopf.ErrorsMode.IGNORED

The current and historic behaviour (the new default) is to treat all errors as temporary until the timeout is reached, or forever until the resource is deleted (if timeout is not set).

Also, a cooldown period between retries can be configured. Previously, it was hard-coded to 60 seconds.

The example with exceptions is changed accordingly to demo the now extended usage.

See the list of commits for detailed step-by-step changes.

Types of Changes

• New feature (non-breaking change which adds functionality)
• Refactor/improvements

Review

List of tasks the reviewer must do to review the PR

• Tests
• Documentation

[zincr]

🤖 zincr found 0 problems , 0 warnings

✅ Large Commits
✅ Approvals
✅ Specification
✅ Dependency Licensing

[zincr]

🤖 zincr found 1 problem , 0 warnings

❌ Approvals
✅ Large Commits
✅ Specification
✅ Dependency Licensing

Details on how to resolve are provided below

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Approvals

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Not enough people have approved this pull request - please ensure that 1 additional user, who have not contributed to this pull request approve the changes.

• ✅ Approved by PR author @nolar
• ❌ 1 additional approval needed
   

[dneuhaeuser-zalando]

should be: "are environment issues" without "the"

[nolar]

Fixed.