chore: added http Spel function category and functions for fcli actions

[kadraman]

Changes made:

• Added new Spel function category http
• Added new SpEL functions base64Decode, base64Encode to util category
• Added new SpEL functions basicAuth, bearerAuth, urlDecode, urlEncode to http category
• Moved uriPart function to category http

All functions are null safe.

Example usage in action YAML (with fixed expression syntax):

Authorization: "${#basicAuth(cli['sonatype-username'], cli['sonatype-password'])}"

I did not change action schema version in gradle.properties

[Copilot]

Pull request overview

Adds a new standard SpEL utility function to help fcli actions generate HTTP Authorization headers for Basic Authentication, enabling easier integration with services that require basic auth credentials.

Changes:

• Added a new #basicAuth(username, password) SpEL function in util category that returns Basic <base64(username:password)>.
• Ensured encoding uses UTF-8 and Base64 encoding; null username/password are treated as empty strings.