doc:merging attribute sources from Confluence(#2287)

[555vedant]

This pull request adds configuration for the CachingPersonAttributeDaoImpl bean to the User Attributes documentation in README.md. The new bean merges user attribute sources, enhancing the flexibility and performance of user data retrieval in uPortal.

-> Changes Made

1. Added a CachingPersonAttributeDaoImpl bean definition to improve attribute merging.
2. Updated the documentation to guide users on configuring multiple user attribute sources effectively.

[555vedant]

Respected Sir/Madam , If all fine then pls dont merge this PR till 1st of OCTOBER , because i am participating into the HACKTOBER fest.

[jonathanmtran]

I think that this would be better located in docs/implement/user-attributes/jdbc.md. Additionally, the myunivCachingPersonDbJdbcAttributeSource example bean should be brought over as well.

[555vedant]

i am just chnaging the Readme.md to its default because added those content into the jdbc.md

[ChristianMurphy]

@555vedant thanks for taking time to contribute.
Yes, we understand you want this to be a part of hacktoberfest, all-caps shout-casing your message repeatedly is not necessary 🙂

[555vedant]

@ChristianMurphy sir thanks

[jonathanmtran]

Per https://hacktoberfest.com/participation/#pr-mr-details

Your PR/MRs must be created between October 1 and October 31 (in any time zone, UTC-12 thru UTC+14)

Since you are looking to participate in Hacktoberfest, I am going to close this PR.
After 1 October, please squash the commits in this branch down to one commit and then submit a new PR

[555vedant]

@ChristianMurphy okay