add many functions provided by the sprig lib

[glehmann]

namely:

typeOf dir toJson hasPrefix trunc wrap untitle regexReplaceAll genSignedCert hasKey clean floor uuidv4 compact date_in_zone tuple date_modify first toPrettyJson sha1sum untilStep splitList pick genPrivateKey slice quote ago date b32enc kindIs pluck randAlphaNum until without max typeIs push genSelfSignedCert regexFind unixEpoch rest abbrevboth nospace biggest mul sub append regexReplaceAllLiteral keys regexMatch round b64enc mod squote nindent set randNumeric trimPrefix min reverse semver coalesce trimAll dateModify dateInZone snakecase b32dec randAscii cat join float64 trimSuffix isAbs values genCA kindOf add1 htmlDate semverCompare initial last div substr repeat splitn abbrev title plural hello list indent ceil sha256sum wrapWith swapcase omit buildCustomCert typeIsLike sortAlpha trimall mergeOverwrite initials env htmlDateInZone toString expandenv int64 camelcase hasSuffix ext trim kebabcase ternary uniq toDate randAlpha b64dec shuffle regexFindAll now dict prepend regexSplit base empty fail derivePassword adler32sum has int unset merge toStrings

a few are NOT imported from sprig, in order to be fully compatible with the older dockerize versions:

contains upper add split default replace atoi lower

[johannesfritsch]

Yes, please! I could really use some of them, namely something to implement startsWith. If this will not be added I will have to switch dockerize for something else.

My need: Have to write some env variables to a file, but only the ones that start with "REACT_APP_"

[mwmahlberg]

I find this interesting, but there should be tests to ensure future versions of sprig do not break compatibility.