refactor(gitlab-changelog): Make url encoding consistent

[rv2673]

Changes:

Behaviour changes

• Slashes are now replaced by %2F instead of lowercases %2f.
• Fully url encode repository name instead of only replacing slashes trough regex. Which means other to be escaped characters will now also be url encoded for changelog calls.

Code changes

• Replace encoding function with builtin url encoding function.

Context:

The url encoding used in changelog calls is different than the url encoding in all other gitlab datasources, which use the builtin encoding function. This PR refactors the code so that this is consistent.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 31.38.4 🎉

The release is available on:

• GitHub release
• 31.38.4

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