feat(input.tail): Add initial_read_offset config for controlling read behavior

[wen-templari]

Summary

This PR add a initial_read_offset config for tail plugin. This option gives user more control over the read behavior.

• It can take following options:

  • beginning -- start reading from the beginning of the file ignoring any persisted offset
  • end -- start reading from the end of the file ignoring any persisted offset
  • saved-or-beginning -- use the persisted offset of the file or, if no offset persisted, start from the beginning of the file
  • saved-or-end -- use the persisted offset of the file or, if no offset persisted, start from the end of the file

• Use saved-or-beginning as default because it matches the previous default from_beginning = false behavior.

• After setting initial_read_offset , the from_beginning config will be ignored.

• Change store offset logic. Now the plugin will always store offset ignoring the from_beginning config.

Checklist

• No AI generated code was used in this PR

Related issues

resolves #16237
replaces #16240

[srebhan]

Thanks @wen-templari for your contribution! I do have some comments in the code. Please remember to run make docs after changing the sample.conf file...

Additionally I want to ask you to deprecate the from_beginning option as it is replaced by the new one...

[srebhan]

Thanks a lot @wen-templari!

[srebhan]

@wen-templari I fixed some small formatting issues. Could you please solve the merge conflict?!?

[wen-templari]

Hi @srebhan, I have resolved the merge conflicts.

[telegraf-tiger]

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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

[wen-templari]

Hi @srebhan, I updated the code to fix initialization on the InitialReadOffset field. Could you please review it again?