Provide minimal custom converters for some examples

For example, Camel Twitter connector examples get a lengthy tweet message format like this with the default `org.apache.kafka.connect.storage.StringConverter`.

> StatusJSONImpl{createdAt=Thu Jan 21 19:40:53 UTC 2021, id=1352340411239559170, text='We released Apache Camel 3.7.1 (LTS) today, a new patch release with 29 fixes and improvements: https://t.co/osOTD4uY5k #apachecamel', source='TweetDeck', isTruncated=false, inReplyToStatusId=-1, inReplyToUserId=-1, isFavorited=false, isRetweeted=false, favoriteCount=37, inReplyToScreenName='null', geoLocation=null, place=null, retweetCount=18, isPossiblySensitive=false, lang='en', contributorsIDs=[], retweetedStatus=null, userMentionEntities=[], urlEntities=[URLEntityJSONImpl{url='https://t.co/osOTD4uY5k', expandedURL='https://camel.apache.org/blog/2021/01/RELEASE-3.7.1/', displayURL='camel.apache.org/blog/2021/01/R…'}], hashtagEntities=[HashtagEntityJSONImpl{text='apachecamel'}], mediaEntities=[], symbolEntities=[], currentUserRetweetId=-1, user=UserJSONImpl{id=1086624104466341888, name='Apache Camel', email='null', screenName='ApacheCamel', location='', description='Apache Camel™ is a versatile open-source integration framework based on Enterprise Integration Patterns from @TheASF', isContributorsEnabled=false, profileImageUrl='http://pbs.twimg.com/profile_images/1090189047367192577/xWt1RFo6_normal.jpg', profileImageUrlHttps='https://pbs.twimg.com/profile_images/1090189047367192577/xWt1RFo6_normal.jpg', isDefaultProfileImage=false, url='https://t.co/cH7LVwWAdJ', isProtected=false, followersCount=1629, status=null, profileBackgroundColor='000000', profileTextColor='000000', profileLinkColor='FAB81E', profileSidebarFillColor='000000', profileSidebarBorderColor='000000', profileUseBackgroundImage=false, isDefaultProfile=false, showAllInlineMedia=false, friendsCount=0, createdAt=Sat Jan 19 13:59:09 UTC 2019, favouritesCount=30, utcOffset=-1, timeZone='null', profileBackgroundImageUrl='http://abs.twimg.com/images/themes/theme1/bg.png', profileBackgroundImageUrlHttps='https://abs.twimg.com/images/themes/theme1/bg.png', profileBackgroundTiled=false, lang='null', statusesCount=326, isGeoEnabled=false, isVerified=false, translator=false, listedCount=28, isFollowRequestSent=false, withheldInCountries=null}, withHeldInCountries=null, quotedStatusId=-1, quotedStatus=null}

It would be great for the examples (if appropriate) to provide a custom converter so that it can simplify how the example looks at work and also demonstrate how the user can customise messages with CKC.