[checkpoint] Update kv split for checkpoint

[ash-darin]

Enhancement

Proposed commit message

This uses a more complex Regex to split the KV pairs in the Checkpoint message.

This is necessary if you use it to process email, as the headers might contain strings of the form:

X-IronPort-AV: E=Sophos;i=\\\"8.18,219,1756234400\\\"; d=\\\"png

"; Sophos

The original regex would regeard both examples as a split, when in reality they are not. Use (negative) lookbehind to box the kv split parameter in.

(?<!\\")(?<="); (?=\w)

lookbehind: (?<=") react to ";
but
negative lookbehind: (?<!\\") do not react to \";

lookahead: (?=\w) expect a character after 1 (one) space: ; abcd

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.

How to test this PR locally

Check your logs/indices if any messages are rejected. Apply fix and check whether numbers go down..

[elasticmachine]

Pinging @elastic/integration-experience (Team:Integration-Experience)

[taylor-swanson]

Could you add a pipeline test to verify the change behaves correctly?

Additionally, the version in manifest.yml needs to be updated to match the changelog (1.41.3)