fix(l1): restore datadir path (#4050)

**Motivation**
PR #4024 changed how we initialize the datadir. Instead of looking for
the database in a path relative to the home directory (ie:
.local/share/datadir on linux) it now looks for it on the path relative
to the current directory (ie: ethrex/datadir). This caused problems when
updating the ethrex commit on currently running ethrex nodes due to the
DB mismatch.
This PR restores the previous behaviour, and has been confirmed to work
as usual on the aforementioned ethrex nodes.
<!-- Why does this pull request exist? What are its goals? -->

**Description**
* Restore where we look for the datadir (relative to home vs current
dir)
<!-- A clear and concise general description of the changes this PR
introduces -->

<!-- Link to issues: Resolves #111, Resolves #222 -->

Closes None, but is needed to continue #1676

Author: fmoletta

cmd/ethrex/utils.rs

@@ -117,6 +117,12 @@ pub fn default_datadir() -> String {
 
 // TODO: Use PathBuf instead of strings
 pub fn init_datadir(data_dir: &str) -> String {
+    let project_dir = ProjectDirs::from("", "", data_dir).expect("Couldn't find home directory");
+    let data_dir = project_dir
+        .data_local_dir()
+        .to_str()
+        .expect("invalid data directory")
+        .to_owned();
     let datadir = PathBuf::from(data_dir);
     if datadir.exists() {
         if !datadir.is_dir() {