Add basic auth generator function

[MatteoVoges]

Proposed Changes

• Added a generator function for basic auth secrets

Usage

The generator function has two optional arguments: ?{ref:path/to/secret||basicauth:username:password}
If the arguments are not specified, a text-string containing 8 characters will be generated.

Examples

• ||basicauth could generate something like dddkfrgl:DDwlFByq as username:password - token
  NOTE: The secret itself is base64 encoded so it will look like ZGRka2ZyZ2w6RER3bEZCeXE=
• |basicauth:user123:key123 would exactly generate user123:key123 as token, so the secret (base64) would be dXNlcjEyMzprZXkxMjM=

Testing and docs

Added test for basic auth generator function.
Updated secret.md as well.

[ramaro]

lgtm @MatteoVoges ! Can you please rebase before we can merge?

[ramaro]

merging! 👍🏼