Replace PAT with secrets.GITHUB_TOKEN in release-please workflow

[Copilot]

The release-please workflow was using a custom PAT (secrets.HCA_RELEASE_PLEASE_TOKEN) which requires manual maintenance. GitHub's built-in secrets.GITHUB_TOKEN provides the same functionality without the overhead.

Changes

• Replace secrets.HCA_RELEASE_PLEASE_TOKEN with secrets.GITHUB_TOKEN in token configuration
• Add workflow_dispatch trigger to enable manual workflow runs
• Remove outdated PAT configuration comments

# Before
token: ${{ secrets.HCA_RELEASE_PLEASE_TOKEN }}

# After  
token: ${{ secrets.GITHUB_TOKEN }}

Aligns with the pattern used in DataBiosphere/data-portal.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update release-please.yml config to use secrets.GITHUB_TOKEN</issue_title>
<issue_description># Overview
We use a PAT to authenticate "release-please", but this is not necessary. Instead, we can use secrets.GITHUB_TOKEN

The file to change:
https://github.com/DataBiosphere/data-browser/blob/main/.github/workflows/release-please.yml

Set up the token similar to
https://github.com/DataBiosphere/data-portal/blob/main/.github/workflows/release-please.yml

Don't change any other release-please config.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update release-please.yml config to use secrets.GITHUB_TOKEN #4597

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