help: Move static/images/help to starlight_help/src/images.

Astro was importing these images and doing it's own processing anyways,
there was not a reason for these images to stay in the static folder.

For channels-and-topics.png, we keep the help center directory as the
source directory for two symlinks since that is where the image is
likely to stay the longest.

static/images/emails/channels-and-topics.png

@@ -1 +1 @@
-../help/channels-and-topics.png
+../../../starlight_help/src/images/channels-and-topics.png

static/images/help/desktop-web-check-icon.svg

@@ -1,3 +0,0 @@
-<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="100%" height="100%" viewBox="0 0 512 512" style="enable-background:new 0 0 512 512;" xml:space="preserve" fill="#5f5ffc">
-    <path d="M448,71.9c-17.3-13.4-41.5-9.3-54.1,9.1L214,344.2l-99.1-107.3c-14.6-16.6-39.1-17.4-54.7-1.8 c-15.6,15.5-16.4,41.6-1.7,58.1c0,0,120.4,133.6,137.7,147c17.3,13.4,41.5,9.3,54.1-9.1l206.3-301.7 C469.2,110.9,465.3,85.2,448,71.9z"/>
-</svg>

static/images/help/desktop-web-plus-icon.svg

@@ -1,3 +0,0 @@
-<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="100%" height="100%" viewBox="0 0 512 512" style="enable-background:new 0 0 512 512;" xml:space="preserve" fill="#b8b8b8">
-    <path d="M459.319,229.668c0,22.201-17.992,40.193-40.205,40.193H269.85v149.271c0,22.207-17.998,40.199-40.196,40.193   c-11.101,0-21.149-4.492-28.416-11.763c-7.276-7.281-11.774-17.324-11.769-28.419l-0.006-149.288H40.181   c-11.094,0-21.134-4.492-28.416-11.774c-7.264-7.264-11.759-17.312-11.759-28.413C0,207.471,17.992,189.475,40.202,189.475h149.267   V40.202C189.469,17.998,207.471,0,229.671,0c22.192,0.006,40.178,17.986,40.19,40.187v149.288h149.282   C441.339,189.487,459.308,207.471,459.319,229.668z"/>
-</svg>

static/images/landing-page/why-zulip/channels-and-topics.png

@@ -0,0 +1 @@
+../../../../starlight_help/src/images/channels-and-topics.png