Add Amazon Bedrock AgentCore to the LLM Observability page

[alaudazzi]

Summary

This PR adds Amazon Bedrock AgentCore to the LLM Observability page and renames various titles.
Fixes #4074

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

[github-actions]

Vale Linting Results

Summary: 3 suggestions found

💡 Suggestions (3)

File	Line	Rule	Message
solutions/observability/applications/llm-observability.md	5	Elastic.Capitalization	'LLM and agentic AI observability' should use sentence-style capitalization.
solutions/observability/applications/llm-observability.md	14	Elastic.Capitalization	'LLM and agentic AI platform observability with Elastic integrations' should use sentence-style capitalization.
solutions/observability/applications/llm-observability.md	28	Elastic.Capitalization	'LLM and agentic AI application observability with APM (distributed tracing)' should use sentence-style capitalization.

[github-actions]

🔍 Preview links for changed docs

• solutions/observability/applications/llm-observability.md

[daniela-elastic]

1. Curious why we are putting Amazon Bedrock AgentCore before Amazon Bedrock. I would have reversed the order since AgentCore is part of Bedrock.
2. Can we put Azure AI Foundry below Bedrock.
3. Arrange order to be:
   Amazon Bedrock
   Amazon Bedrock AgentCore
   Azure AI Foundry
   Azure OpenAI
   GCP VertexAI
   OpenAI
   Feel free to address, not need for further approvals

[daniela-elastic]

Pls fix Agent -> Agentic (see comments). No need for further approvals

[florent-leborgne]

We don't need to capitalize all of these terms if we refer to the branding guidelines - and we should try to keep that first H2 title more specific
Otherwise LGTM!

for reference: https://brand.elastic.co/302f66895/p/194a3b-writing-style-guide/t/19954f

[florent-leborgne]

LGTM