Add an IndexedDB backend for the certificate chain cache in the WASM client

[jpraynaud]

Why

We need to provide some WASM support for the certificate chain cache that survives restarts. We can't use the file implementation in WASM and given the storage size of the certificates, we need to use IndexedDB for implementation.

What

Add a IndexedDbCertificateVerifierCache implementation of CertificateVerifierCache in mithril-client for non-WASM targets.

How

• Store each certificate in a the indexed DB
• Use a space for the committed cache
• Use a space by certificate chain validation id for staging
• Upon committing, the staged certificates are moved the to the committed cache (atomic moves with transactions)
• Adapt the nightly tests to use the cache (ci-test)