fix: correct the consistency checker's config "type" validation

[tonyandrewmeyer]

Some small corrections to the consistency checker's validation of the type field in config:

1. "integer" is not valid (at least in Juju 3.4.0), so remove it
2. "number" is not valid (at least in Juju 3.4.0), so remove it
3. "float" is missing, so add it
4. This is currently undocumented (that should be fixed soon) but "type: secret" is valid from Juju 3.4 onwards, so add it (conditionally on the Juju version)

Adjust tests to match.

See also canonical/operator#1166 for type:secret issue in Harness.

[benhoyt]

Oh, and thanks for this, Tony -- appreciated!

[PietroPasotti]

Couple of nits and grits but it looks good!
Might be a good chance to get rid of that commented-out attrs question mark too?
I'm sure there was an attrs type in some document at some point, but I can't find it anymore so we can probably safely get rid of it.

[PietroPasotti]

Noice! thanks a lot :)