gcore: change API domain

[mikalai-dzemidzenka]

Hi, this PR for https://gcore.com/dns/ PR contains update of DNS API URL, change name to G-Core and update links to docs.

[ldez]

For the context:

• https://taz.de/Russia-Today-von-Luxemburger-Firma-unterstuetzt/!5913875/
• https://taz-de.translate.goog/Russia-Today-von-Luxemburger-Firma-unterstuetzt/!5913875/?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=fr&_x_tr_pto=wapp
• https://chronicle.lu/category/ict-services/44400-gcore-labs-sa-refutes-claims-it-bypasses-sanctions-to-disseminate-russian-propaganda

I'm not here to judge but I want clear and transparent information.

No companies want to break their API, their main domain, or their website, and you are from Belarus, this domain change seems to be not so neutral.