Add support for multiple messages for the update command

Summary

Renovate could batch multiple dependency updates into a single MR, as such the update command needs to be able to log multiple changelog messages in a single invocation

Example Usage

changelog-parser update -c CHANGELOG.md -t minor -m 'Update github.com/stretchr/testify from v1.10.0 to v1.11.1' -m 'Update gitlab.com/gitlab-org/security-products/analyzers/ruleset/v3 from v3.3.2 to v3.3.3' -m 'Update go from 1.23.1 to 1.25.1' -m 'Update golang from 1.23.2 to 1.25.1' -m 'Update python from 3.12 to 3.13' -m 'Update registry.gitlab.com/security-products/post-analyzers/tracking-calculator from 2.6.0 to 2.8.0' -m 'Update registry.gitlab.com/security-products/post-analyzers/tracking-calculator from 2.6.0 to 2.8.0'

This will generate an entry like this:

## v1.3.0
- Update github.com/stretchr/testify from v1.10.0 to v1.11.1 (!{{MERGE_REQUEST_ID}})
- Update gitlab.com/gitlab-org/security-products/analyzers/ruleset/v3 from v3.3.2 to v3.3.3 (!{{MERGE_REQUEST_ID}})
- Update go from 1.23.1 to 1.25.1 (!{{MERGE_REQUEST_ID}})
- Update golang from 1.23.2 to 1.25.1 (!{{MERGE_REQUEST_ID}})
- Update python from 3.12 to 3.13 (!{{MERGE_REQUEST_ID}})
- Update registry.gitlab.com/security-products/post-analyzers/tracking-calculator from 2.6.0 to 2.8.0 (!{{MERGE_REQUEST_ID}})
- Update registry.gitlab.com/security-products/post-analyzers/tracking-calculator from 2.6.0 to 2.8.0 (!{{MERGE_REQUEST_ID}})

Related Issue

Replace sast-analyzer-deps-bot with renovate (gitlab-org/gitlab#557439)