docs: Implement FAQ page, default values in Cue + fix sidebar and titles

Move faq pages from guide to specific FAQ page, shown as per tailscale format.
Custom in-house logic implemented because Docusaurus doesn't manage it

Signed-off-by: guillaume <guillaume.derouville@gmail.com>

docs/faq/1229-empty-buildkit-cache.md

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+---
+slug: /1229/empty-buildkit-cache
+displayed_sidebar: europa
+---
+
+# Empty BuildKit's cache
+
+There are two ways of emptying the BuildKit cache:
+
+- Run your action with the `--no-cache` option:
+
+```console
+dagger do <your-action> --no-cache
+```
+
+- Stop and remove the buildkitd container and remove its associated volume:
+
+```console
+docker stop dagger-buildkitd ; docker rm dagger-buildkitd ; docker volume rm dagger-buildkitd
+```
+
+In 99.9% of the cases, the first solution is enough

docs/faq/1230-better-logs.md

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+---
+slug: /1230/better-logs
+displayed_sidebar: europa
+---
+
+# Log formats
+
+Dagger exposes 2 logging format options:
+
+- `--log-format auto|plain|tty|json`
+
+The default mode is `auto`. If you want to keep each actions' logs, use the `plain` mode
+
+- `--log-level panic|fatal|error|warn|info|debug|trace`
+
+`debug` is useful to check whether an explicit dependency has been found between two actions.
+
+You can also export these options as env variables:
+
+```console
+export DAGGER_LOG_FORMAT="plain"
+export DAGGER_LOG_LEVEL="debug"
+```

docs/faq/1231-always-execute.md

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+---
+slug: /1231/always-execute
+displayed_sidebar: europa
+---
+
+# Always executing an action
+
+Dagger implemented a way to tell Buildkit not to rely on cache for a specific action.
+
+The `docker.#Run` and `core.#Exec` definitions have an `always` field:
+
+```cue
+// If set to true, the cache will never be triggered for that specific action.
+always: bool | *false
+```
+
+Any package composed on top of it (`bash.#Run` for example) also exposes this field as it will inherit it from `docker.#Run`:
+
+```cue
+test: bash.#Run & {
+    always: true
+    ...
+}
+```

docs/faq/1232-chain-actions.md

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+---
+slug: /1232/chain-actions
+displayed_sidebar: europa
+---
+
+# Chaining actions
+
+Dependencies are materialized at runtime, when your Cue files are parsed and the corresponding DAG gets generated:
+
+```cue
+// Prerequisite action that runs when `test` is being called
+_dockerCLI: alpine.#Build & {
+    packages: {
+        bash: {}
+    }
+}
+
+// Main action
+foo: bash.#Run & {
+    input: _dockerCLI.output // <== CHAINING of action happening here
+    always: true
+    script: contents: #"""
+        echo "bonjour"
+        """#
+}
+```
+
+On above example, `_dockerCLI` gets executed first, as the corresponding DAG shows that it is required for the action `foo` to be processed.
+
+This is the `input-output` model: `foo`'s input is `_dockerCLI`'s output.
+
+We currently don't support explicit dependencies at the moment (one of our top priority). But, if you need one, here is how your can hack your way around it:
+
+```cue
+foo: bash.#Run & {
+    input: _dockerCLI.output
+    always: true
+    script: contents: #"""
+        echo "bonjour"
+        """#
+}
+
+// Main action
+bar: bash.#Run & {
+    input: _dockerCLI.output
+    always: true
+    script: contents: #"""
+        echo "bonjour"
+        """#
+    env: HACK: "\(test.success)" // <== HACK: CHAINING of action happening here
+}
+```
+
+`foo` and `bar` are similar actions. I don't want to rely on the `input-output` model but still want to force a dependency between them. The easiest way is to create an environment variable that relies on the other action's success

docs/faq/index.md

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+---
+slug: /faq
+displayed_sidebar: europa
+---
+
+# FAQ
+
+```mdx-code-block
+import DocCardList from '@theme/DocCardList';
+import {useDocsVersion} from '@docusaurus/theme-common';
+
+export const FaqItems = () => {
+    {/* access root category object from Docusaurus */}
+    const docsVersion = useDocsVersion();
+    {/* customProps object retrieved from sidebar.js */}
+    const faqItem = docsVersion.docsSidebars.europa.filter(item => item.label === 'FAQ');
+    {/* Return custom FAQ Items array */}
+    const customPropsItem = faqItem[0].customProps.items.map(customPropsItem => {
+        const result = Object.values(docsVersion.docs).filter(item => item.id === customPropsItem.docId)[0]
+        if(result)
+            return {
+                type: "link",
+                label: result.title,
+                description: result.description,
+                href: customPropsItem.href,
+                docId: customPropsItem.docId
+            }
+    })
+    return <DocCardList items={customPropsItem}/>
+}
+
+<FaqItems />
+```