SEO: add canonicals and change meta titles

[NikitaSavik]

1.For internal hrefs:

• https://eth.blockscout.com/
• https://eth.blockscout.com/txs
• https://eth.blockscout.com/ops
• https://eth.blockscout.com/verified-contracts
• https://eth.blockscout.com/name-domains
• https://eth.blockscout.com/withdrawals
• https://eth.blockscout.com/tokens
• https://eth.blockscout.com/stats
• https://eth.blockscout.com/api-docs
• https://eth.blockscout.com/graphiql
• https://eth.blockscout.com/gas-tracker
• https://eth.blockscout.com/apps

Add 'canonical' parameter, e.g.
<link rel="canonical" href="https://eth.blockscout.com/" />

2. Change metatag Title

Page - 'Duplicate Meta Titles' (please ask @NikitaSavik for table URL)

• For root pages, change the title according to the table
• Change 'Ethereum' with chain name

3. Change H1 Title

Page - 'Duplicate H1 and Title'

• For root pages, change the H1 title according to the table (column \new h1)
• Change 'Ethereum' with chain name

[NikitaSavik]

@maikReal - to provide schema for H2 for Dappscout pages, e.g. Dappscout - {Category}

[tom2drum]

Decided not to implement any changes on the Marketplace page.
All page titles (<h1>) will be changed only if variable NEXT_PUBLIC_SEO_ENHANCED_DATA_ENABLED is set to true