FINERACT-2310: collate and improve security documentation

* fix various typos, spacing, formatting issues
* fix links to legacy docs in API docs
* update keycloak oauth dev instructions
* update default oauth URL for latest Keycloak
* use consistent quoting in oauth docs (single quotes)
* use asciidoc auto-enumerated lists whenever possible
* migrate security topics from readme into asciidoc: oauth, 2FA, HTTPS
* move :hardbreaks: setting to config file so all config settings are in one place. (I think it's fine that `license.adoc` will use hardbreaks -- that's how the plain text version is formatted so it should look more familiar)
* add intro to security chapter
* migrate in Securing Fineract wiki content from https://cwiki.apache.org/confluence/display/FINERACT/Securing+Fineract
* just say "oauth" (not "oauth2") to conform terminology throughout docs -- OAuth 2.0 is just the latest version
* cross-ref HTTPS section from Securing Fineract
* reposition hardening options as tips
* see also: https://lists.apache.org/thread/81qdxttffp6wn23c48zvk93hc13373qv
* simplify/clarify example oauth curl requests
  * Testing just now and I didn't need --location.
  * Also I imagine folks will need --insecure with the self-signed default cert in dev.
* don't change default oauth URL
  * no surprises for existing deployments
  * clarifies the keycloak v26 example

fineract-doc/src/docs/en/config.adoc

@@ -25,6 +25,7 @@
 :email: dev@fineract.apache.org
 :checkedbox: pass:normal[{startsb}✔{endsb}]
 :table-stripes: even
+:hardbreaks:
 
 // ifeval::["{draft}"=="true"]
 // :title-page-background-image: image:{commondir}/images/draft.svg[position=top]
@@ -43,4 +44,4 @@ ifdef::env-github[]
 :important-caption: :heavy_exclamation_mark:
 :caution-caption: :fire:
 :warning-caption: :warning:
-endif::[]
+endif::[]