Fix Issues in Existing Pattern

[rajavaid77]

• Corrected default values in template.yml for AOSS resources
• Added requirements.txt and Metadata section to LayerVersion to enable layer build using SAM
• Updated README to update dependency build step to use sam build
• Updated IndexCreationLambda function to add field mappings to newly created AoSS Index

PR #2289

[julianwood]

Added, thanks