…mains.

pkg/fqdn: Adding ** matchpattern

The ** in matchpattern allows a short notation of multilevel subdomains

Instead of the rules with listed subdomains:

rules:
  dns:
    - matchPattern: '*.cluster.local'
    - matchPattern: '*.*.cluster.local'
    - matchPattern: '*.*.*.cluster.local'
    - matchPattern: '*.*.*.*.cluster.local'
    - matchPattern: '*.*.*.*.*.cluster.local'
    - matchPattern: '*.*.*.*.*.*.cluster.local'
    - matchPattern: '*.*.*.*.*.*.*.cluster.local'
    - matchPattern: '*.*.*.*.*.*.*.*.cluster.local'

egress:
  - toFQDNs:
    - matchPattern: '*.cilium.io'
    - matchPattern: '*.*.cilium.io'
    - matchPattern: '*.*.*.cilium.io'
    - matchPattern: '*.*.*.*.cilium.io'
    - matchPattern: '*.*.*.*.*.cilium.io'
    - matchPattern: '*.*.*.*.*.*.cilium.io'
    - matchPattern: '*.*.*.*.*.*.*.cilium.io'
    - matchPattern: '*.*.*.*.*.*.*.*.cilium.io'

the following policy can be used in a simpler form:

rules:
  dns:
    - matchPattern: '**.cluster.local'

egress:
  - toFQDNs:
    - matchPattern: '**.cilium.io'

Changelog:
Modified the code and added tests.
Updated language.rst.
Updated matchpattern.go.
Added and updated doc files.
Updated language.rst with a security note.
Double asterisk is allowed at the beginning of the domain only.

Signed-off-by: Piotr Jablonski <[email protected]>

```release-note
The ** in matchpattern allows a short notation of multilevel subdomains,
eg. **.cilium.io matches a.cilium.io, a.b.cilium.io, a.b.c.cilium.io, etc.

This feature can break current configuration if a double asterisk was used inside of FQDN, eg. cil**.io
Before this enhancement two or more directly adjacent asterisks meant the same - a single asterisk, eg. cil**.io == cil*.io
The correct usage of the asterisk before this enhancement should be a single presence between other characters, eg. c*m.io, *.cil*.io
With this enhancement the correct usage of the single asterisk does not change
A double asterisk must be at the beginning of the FQDN string only, eg. **.cilium.io
The single and double asterisk can be present in the same FQDN if they are separated by a dot directly or indirectly, eg. **.*lium.io, **.cili*.io
```