docs: add node101 to MultiversX API external providers

[girginomer10]

Description of the pull request (what is new / what has changed)

Add node101's managed dedicated MultiversX node service to External Providers, following the existing Kepler description-and-link format. Describe REST API and gRPC access, operational features, and archive/testnet options available on request. Explicitly state that the service requires a paid plan and has no free public endpoint or free tier.

Sources:

• https://node101.io/en/rpc/multiversx
• https://node101.io/en/rpc

Did you test the changes locally ?

• yes
• no

Checked the entry against the current product page and existing provider format. Only the External Providers section changes; local patch application and exact-insertion comparison verified. Full site build and customer endpoint testing have not been run.

Did you regenerate static/llms.txt and static/llms-full.txt ? (happens at build time)

• yes
• no

Which category (categories) does this pull request belong to?

• document new feature
• update documentation that is not relevant anymore
• add examples or more information about a component
• fix grammar issues
• other

Target: development, as required by the repository contribution guide.

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