fix(agent): Restore setup order of stateful plugins to Init() then SetState()

[srebhan]

Summary

PR #15170 changed the startup sequence of stateful plugins from Init -> SetState to SetState -> Init and in turn broke all stateful users (inputs.tail, inputs.docker_log, inputs.win_eventlog and processors.dedup) to make starlark state-persistence work.

As a code sequence of Init -> SetState is the expected behavior and what works for all previous users, this PR restores the old order and fixes common.starlark to also work with this sequencing. The PR furthermore adds unit-tests where possible to make sure the sequence works. Last but not least, the PR updates the spec and also defines the shutdown order to be Close/Stop -> GetState.

Checklist

• No AI generated code was used in this PR

Related issues

resolves #16037

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_arm64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

☺️ This pull request doesn't significantly change the Telegraf binary size (less than 1%)

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz