New macros added for encoding and decoding strings for url (url_encode, url_decode)

[D1111111]

resolves #1013

Problem

There is no reliable way to encode/decode strings for url. There is an open issue here: https://github.com/dbt-labs/dbt-utils/issues/1013

Solution

A macro used to encode/decode url strings

Checklist

• [x] This code is associated with an issue which has been triaged and accepted for development.
• [x] I have read the contributing guide and understand what's expected of me
• [x] I have run this code in development and it appears to resolve the stated issue
• [x] This PR includes tests, or tests are not required/relevant for this PR
• [x] I have updated the README.md (if applicable)