Use anyhow more idiomatically (#31052)

https://github.com/zed-industries/zed/issues/30972 brought up another
case where our context is not enough to track the actual source of the
issue: we get a general top-level error without inner error.

The reason for this was `.ok_or_else(|| anyhow!("failed to read HEAD
SHA"))?; ` on the top level.

The PR finally reworks the way we use anyhow to reduce such issues (or
at least make it simpler to bubble them up later in a fix).
On top of that, uses a few more anyhow methods for better readability.

* `.ok_or_else(|| anyhow!("..."))`, `map_err` and other similar error
conversion/option reporting cases are replaced with `context` and
`with_context` calls
* in addition to that, various `anyhow!("failed to do ...")` are
stripped with `.context("Doing ...")` messages instead to remove the
parasitic `failed to` text
* `anyhow::ensure!` is used instead of `if ... { return Err(...); }`
calls
* `anyhow::bail!` is used instead of `return Err(anyhow!(...));`

Release Notes:

- N/A

crates/collab/src/main.rs

@@ -1,4 +1,4 @@
-use anyhow::anyhow;
+use anyhow::{Context as _, anyhow};
 use axum::headers::HeaderMapExt;
 use axum::{
     Extension, Router,
@@ -138,11 +138,11 @@ async fn main() -> Result<()> {
                             .config
                             .llm_database_url
                             .as_ref()
-                            .ok_or_else(|| anyhow!("missing LLM_DATABASE_URL"))?;
+                            .context("missing LLM_DATABASE_URL")?;
                         let max_connections = state
                             .config
                             .llm_database_max_connections
-                            .ok_or_else(|| anyhow!("missing LLM_DATABASE_MAX_CONNECTIONS"))?;
+                            .context("missing LLM_DATABASE_MAX_CONNECTIONS")?;
 
                         let mut db_options = db::ConnectOptions::new(database_url);
                         db_options.max_connections(max_connections);
@@ -287,7 +287,7 @@ async fn setup_llm_database(config: &Config) -> Result<()> {
     let database_url = config
         .llm_database_url
         .as_ref()
-        .ok_or_else(|| anyhow!("missing LLM_DATABASE_URL"))?;
+        .context("missing LLM_DATABASE_URL")?;
 
     let db_options = db::ConnectOptions::new(database_url.clone());
     let db = LlmDatabase::new(db_options, Executor::Production).await?;