Add STRING input validator

[yuri1969]

This PR adds a regex-based validation for the STRING inputs. The pattern is defined by input's newly added validator property.

inputs:
  - name: my-upper-case-value
    type: STRING
    validator: [A-Z]+

This PR deals with the STRING inputs only since these are frequent & variable.

Naming, etc. should be reviewed to fit in.

close #1122

[loicmathieu]

@yuri1969 thanks for your PR.

I update it to allow more flexible validation by allowing to validate all input types with differents validation properties and enabling the UI to be aware of this validation.
This is a first step as only String are validated for now but we forsee validating more types (for ex number with minand max properties) and the UI part is not yet done.

[yuri1969]

@loicmathieu Great, adding type-specific validation implementations should be easy now.

[loicmathieu]

I rebased the branch onto master as there was a strange test error.

We will discuss internally if we merge this one as is or if we take the opportunity to add more constraints.

[tchiotludo]

Minor change for seems to be good stuff anyway and there is missing change on webserver unit test

[loicmathieu]

@yuri1969 thanks a lot for your contribution, it is now merged and will be included in Kestra 0.9.0 !

I created two issue to continue on the subject to have a complete input validation in Kestra.