Migrate from opentelemetrybot to otelbot in GitHub workflows

[Copilot]

This PR migrates all GitHub workflows from using the deprecated opentelemetrybot user account to the new otelbot GitHub App, as requested in the migration initiative.

Changes Made

.github/workflows/release-please.yml

• Updated git config to use otelbot instead of opentelemetrybot
• Updated email from [email protected] to [email protected]

.github/workflows/update-otel-deps.yaml

• Replaced token authentication: Migrated from secrets.OPENTELEMETRYBOT_GITHUB_TOKEN to GitHub App token generation using actions/create-github-app-token@df432ceedc7162793a195dd1713ff69aefc7379e
• Eliminated fork-based workflow: Since otelbot is a GitHub App and doesn't have forks, removed the fork creation and upstream sync steps
• Switch to branch-based workflow: Now pushes directly to branches on the main repository prefixed with otelbot/
• Split responsibilities: Uses secrets.GITHUB_TOKEN for pushing branches and the otelbot App token for creating PRs (to ensure workflows are triggered)
• Updated git config to use the new otelbot identity

Key Technical Changes

The most significant change is in update-otel-deps.yaml where the workflow previously:

1. Forked the repository to opentelemetrybot/opentelemetry-js-contrib
2. Synced with upstream
3. Made changes and created PR from the fork

Now it:

1. Generates an otelbot App token
2. Works directly on the main repository
3. Creates a branch prefixed with otelbot/
4. Uses different tokens for pushing vs PR creation to maintain proper workflow triggering

This ensures compatibility with the GitHub App model while maintaining all existing functionality.

Fixes #32.

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