Improve Lua code to get current version

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### How are you using the lua-language-server?

NeoVim

### Which OS are you using?

Other

### What is the issue affecting?

Other

### Expected Behaviour

I would like to get the current version for lua-language-server without `changelog.md` file.

Improve Lua code in `script/version.lua` to get current version (last Git tag).

### Actual Behaviour

When a contributor packages lua-language-server for a distribution (Linux or BSD), the `changelog.md` file is not always included.

In `script/version.lua` file, the current version is defined (function `loadVersion`) with parsing of the `changelog.md` file. **If this file is not present, the returned version is `Unknown`**.

It will be better to get the current version without parsing of `changelog.md` file => get version from the last Git tag or define the current version in `script/version.lua` file.

### Reproduction steps

N/A

### Additional Notes

_No response_

### Log File

_No response_

Start in script/version.lua at loadVersion and inspect how the current version is derived from changelog.md. Reproduce the packaging case with changelog.md absent, then verify the version comes from the last Git tag or an explicitly defined value instead of returning Unknown.

Written by the indexing model from the issue text.