[Filebeat][New Fileset] Cisco AMP (#22768)

* initial stash for cisco amp

* stashing more cisco amp changes

* stashing httpjson v2 type config and merging with master

* stashing amp changes

* updating fields.go

* first finalized MVP for Cisco AMP

* added changelog

* This commit resolves most of the comments made to the PR

* updating pipeline based on PR feedback and comments

* updating field mapping and docs based on PR comments

CHANGELOG.next.asciidoc

@@ -819,6 +819,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Added `alternative_host` option to google pubsub input {pull}23215[23215]
 - Added username parsing from Cisco ASA message 302013. {pull}21196[21196]
 - Added `encode_as` and `decode_as` options to httpjson along with pluggable encoders/decoders {pull}23478[23478]
+- Added support for Cisco AMP API as a new fileset. {pull}22768[22768]
 - Added `application/x-ndjson` as decode option for httpjson input {pull}23521[23521]
 - Added `application/x-www-form-urlencoded` as encode option for httpjson input {pull}23521[23521]
 - Move aws-s3 input to GA. {pull}23631[23631]