fix: improve validation of host/domain set name

[andre8244]

Improve validation of domain sets and host sets:

• Create/edit domain set: ensure domain names contained in the domain set are syntactically valid
• Create/edit domain set: ensure that the total characters length of all domain names doesn't exceed 1024
• Create/edit domain set or host set: ensure host set / domain set name starts with a letter and contains only letters and numbers

Ref:

• Objects: cannot use domainset name that starts with a number nethsecurity#876
• Domain set objects over 1024 bytes crash Dnsmasq nethsecurity#877