Fix url concatenation for dev mode with origin set in server options

[dknibbe]

• Quick Checklist

• [x] I have read the contributing guidelines

• [ ] I have written new tests, as applicable (for bug fixes / features)

• [ ] Docs have been added / updated (for bug fixes / features)

• [ ] I have added a changeset, if applicable

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) This change contains a bug fix for the feature introduced in pull request #690. The server origin option usually contains a protocol scheme identifier followed by a double slash, e.g. "http://localhost:1234". Nodes POSIX path implementation is not meant to join URLs, which means the double slash is converted to a single slash, resulting in an invalid URL, e.g "http:/localhost:1234". Using url-join instead ensures the result will be a valid URL.

• Other information: Added new dependency: url-join, which seams to be the safest option

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: ead219f3c557f706b957c0716746cc67e0312fca

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | --------------- | ----- | | vite-imagetools | Patch |

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.69%. Comparing base (31c14f2) to head (ead219f). Report is 4 commits behind head on main.

Files	Patch %	Lines
packages/vite/src/index.ts	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #732 +/- ## ========================================== - Coverage 95.69% 95.69% -0.01% ========================================== Files 33 33 Lines 1278 1277 -1 Branches 224 224 ========================================== - Hits 1223 1222 -1 Misses 55 55 ``` | [Flag](https://app.codecov.io/gh/JonasKruckenberg/imagetools/pull/732/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Kruckenberg) | Coverage Δ | | |---|---|---| | [imagetools-core](https://app.codecov.io/gh/JonasKruckenberg/imagetools/pull/732/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Kruckenberg) | `95.69% <0.00%> (-0.01%)` | :arrow_down: | | [vite-imagetools](https://app.codecov.io/gh/JonasKruckenberg/imagetools/pull/732/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Kruckenberg) | `95.69% <0.00%> (-0.01%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jonas+Kruckenberg#carryforward-flags-in-the-pull-request-comment) to find out more.

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