[IDEV-1964_1988] Implement nad and domaindiscovery feed; update readme docs

[briluza]

Please label this PR with one of the following labels, depending on the scope of your change:

• Enhancement

Proposed commit message

Implemented Newly Active Domains and domaindiscovery feed.
Please explain:

• WHAT: Added datastream, ingest pipeline, fields and transforms for DomainTools Newly Active Domains and DomainDiscovery feed.
• WHY: Provide more useful feeds from DomainTools

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Author's Checklist

• DomainTools Newly Added Domains feed
• DomainTools Domain Discovery feed

How to test this PR locally

Install and configure DomainTools integration. Search for the following feed results:

• data_stream.dataset: "ti_domaintools.nad_feed"
• data_stream.dataset: "ti_domaintools.domaindiscovery"

Related issues

N/A

Screenshots

[wesleya]

really amazing job Bri!