Add keywords to multiple documentation files for improved SEO and discoverability

[barbaraperic]

Description

The intention of this PR is to enhance the likelihood that these pages are surfaced more effectively in both external search engines and GitHub’s internal search.

Search queries and suggestion for 1st result in Quick Find

Table also available in the ticket - link here

eventSearchQuery	eventsCount	visitorsCount	1st result	Suggestion for the 1st result
gas	12	7	Gas	https://docs.filecoin.io/smart-contracts/filecoin-evm-runtime/how-gas-works Would be better than the JSON-RPC reference
staking	11	10	Networks	This should point to Glif or a page about defi staking
stake	8	7	State	This should point to Glif or a page about defi staking
snapshot	8	7	Callibration	https://lotus.filecoin.io/lotus/install/start-lotus/#download-snapshot I realise this isn’t on docs.filecoin.io but I forgot this aria2c -x5 https://forest-archive.chainsafe.dev/latest/mainnet/ command all the time and need it
fil	7	5	Filecoin.sol	https://docs.filecoin.io/basics/assets/the-fil-token

Important Note

1. Please note that these changes do not guarantee that the targeted pages will be prioritized in internal search results. As stated in the documentation:
   “We do not currently support the ability to prioritize certain content in Quick find results.”

Adding keywords may help with SEO, but for true prioritization within internal search, we would need to consider content rework.

2. Regarding the snapshot comment - I've asked Claude to integrate the command instructions in the content, please double check 😅