SETUP_ENSURE_IMPORTED_PRV_MATCH_LDAP_PUB client configuration with ldap-relay + look up public keys using ldap-relay

[tomholub]

For #768 you will need a new endpoint ldap-relay like was used here FlowCrypt/flowcrypt-browser#4609 . However, the client that was to use this functionality did not deploy android yet, due to other blocking issues. Therefore we can file a new issue for this, but don't have to work on it until we see renewed interest in this.

Originally posted by @tomholub in #1984 (comment)

[tomholub]

@martgil the page at https://flowcrypt.com/docs/technical/enterprise/configuration/client-configuration.html still shows USE_LEGACY_ATTESTER_SUBMIT but we have transitioned to SETUP_ENSURE_IMPORTED_PRV_MATCH_LDAP_PUB, please replace it there, describing what it does per issue FlowCrypt/flowcrypt-browser#4609 and per the implementation on browser.

Then update the table in docs that shows differences between clients as follows:

• only browser supports SETUP_ENSURE_IMPORTED_PRV_MATCH_LDAP_PUB
• only browser looks up public keys on LDAP servers