Quarkus style enhancements: Security overview doc

[michelle-purcell]

Ref #QDOCS-33

First iteration of edits to enhance the SECURITY ARCHITECTURE AND GUIDES guide and apply some of the recently agreed Quarkus style guidelines as described in the Quarkus contributor guide.

[michelle-purcell]

@sberyozkin - I completed a first pass at editing the main overview page in the as-is structure. I have some questions about the content too. Thanks :-)

[michelle-purcell]

@sheilamjones - Hey Sheila, thanks for flagging the overlap with PR #27176. I made a very minor tweak to the OIDC section that you already perfected, mainly to move the links into a table. What do you think? I can reverse if this breaks what you had agreed with SMEs. Thanks :-)

[sberyozkin]

Thanks for a quality PR, @michelle-purcell, I left a few minor suggestions but overall it all looks very good IMHO

[michelle-purcell]

@sberyozkin - Thank you so much for your review and feedback. I have applied all of your suggestions and fixed the other comments.

[sberyozkin]

Thanks @michelle-purcell :-)

[sberyozkin]

@gsmet Hi Guillaume, not sure why the bot has added an agroal label, have a look please