docs: add dedicated session management guide

[Adii-45]

Which problem is this PR solving?

Closes #114

This PR adds dedicated documentation for browser session management to improve discoverability and provide a more comprehensive reference than the existing SDK README!

Previously, session management was only documented as a brief section inside packages/sdk/README.md, making it difficult for users to understand the available APIs, lifecycle, configuration options, extension points, and implementation details!

Short description of the changes

Added

• A new docs/session-management.md guide covering:
  • Session overview
  • Quick start
  • Session lifecycle
  • SessionManager configuration
  • Built-in implementations
  • Registering session processors
  • Observing session lifecycle
  • Custom SessionStore implementations
  • Custom SessionProvider implementations
  • Known limitations
  • Related references

Updated

• Simplified the Sessions section in packages/sdk/README.md by keeping it focused on quick-start usage and linking to the new dedicated guide for detailed documentation.
• Added a new Documentation section to the repository README.md linking to:
  • Session Management
  • Browser Events
  • Navigation Event

This keeps detailed documentation centralized under the docs/ directory while preserving a concise onboarding experience in the SDK README.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Verified all Markdown links resolve correctly
• Reviewed the documentation for accuracy against the current implementation
• Confirmed no runtime code or public APIs were modified
• Ran the existing test suite (npm test) to ensure no regressions

Checklist

• I followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[overbalance]

When we pass our own processors here but no exportConfig, the SDK does not add an OTLP exporter (the check in startTracesSdk.ts and startLogsSdk.ts is !config.processors || config.exportConfig). So this Quick Start sets session.id on spans and logs but never exports them. @martinkuba what do you think?

Suggested change

	serviceName: 'my-service',
	serviceName: 'my-service',
	exportConfig: { url: 'https://your-collector.example.com' },

[overbalance]

Following up, this is the only thread here still open. Sorry, I bundled two different things into one comment, which is probably why it stalled.

For the doc: the Quick Start passes processors without exportConfig, and the SDK only adds the OTLP exporter when !config.processors || config.exportConfig (startTracesSdk.ts:51, startLogsSdk.ts:58), so as written the example sets session.id but never exports anything. Adding exportConfig makes the example work, so let's just do that and not block on anything else.

For whether the SDK should keep the default exporter when processors are passed: that is a separate SDK question and does not belong on a docs PR. I opened #376 for it, so this one can move.

[Adii-45]

@overbalance Just a small bump on this 😄

I've addressed all of the requested documentation changes in the latest commit!

The only remaining discussion is the Quick Start example regarding exportConfig, where I was waiting for guidance since it was tagged for @martinkuba's input.

If you'd prefer me to update the example now, I'm happy to make that change as well. Otherwise, I'll wait for the decision on that discussion!

Whenever you have a chance, I'd appreciate another look. Thanks!