add regex parser

[alimousazy]

Required for all PRs:

• CHANGELOG.md updated
• [ x] Sign CLA (if not already signed)
• README.md updated (if adding a new plugin)

Add new input parser called REGEX, this will allow for creating metrics from non-formated input stream like raw log file. currently it support two model counting matches or extract value. Counting matches works by counting matches of REGEX and report it as a field, while Extract value use capture group to collect field name and value.

[inputs.tail.regex_expr]
request_type = ["GET", "POST", "PUT"]
request_duration = ["(RequestDuration)=([0-9]+)"]

This will create two metrics, the first one is request_type contain a count for GET, POST and PUT occurrence in the file, the second is request_duration metric which will have one field called RequestDuration with extracted duration from REGEX file

[sparrc]

thanks for the work @alimousazy but I am currently working on a logparser implementation in PR #1320