[Doc] Revamp example gallery (#42862)

updates the docs build system to change the way the example gallery is created.

- Examples are now specified in yaml format, regularizing the metadata for each example in each ray library
- Each ray library has an example page that is constructed from its corresponding yaml data
- The example gallery itself is built using all ray library example yaml input data, meaning that individual ray library example pages no longer get out of sync with what is in the example gallery
- As a result of changing the way that ray libraries store their examples, I had to change many of the the references to the ray library examples pages. The content of the example pages has not been changed. These changes are responsible for the majority of the files touched here.
- A second impact of the changes here is that because some of the example pages were being included in toctrees before and now they are not, is that they need to be marked as orphaned. This has been done where necessary, but in particular in the .ipynb files this is actually done in the metadata of the file.
- Capitalize "Example Gallery" in the top navigation bar

---------

Signed-off-by: pdmurray <peynmurray@gmail.com>
Co-authored-by: Lonnie Liu <95255098+aslonnie@users.noreply.github.com>

doc/.gitignore

@@ -15,3 +15,8 @@ source/data/api/doc/
 source/cluster/running-applications/job-submission/doc/
 source/serve/api/doc/
 source/workflows/api/doc/
+
+# Ignore generated examples files
+source/data/examples.rst
+source/train/examples.rst
+source/serve/examples.rst

doc/source/_static/css/custom.css

@@ -386,3 +386,11 @@ table.autosummary tr > td:first-child > p > a > code > span {
 .query-param-ref-wrapper p {
   margin: 0;
 }
+
+/* Styles for tables in example pages */
+.table.example-table {
+  table-layout: fixed;
+}
+.table.example-table th:first-child {
+  width: 30%;
+}