feat: improve footer

- use icon & tooltip for social links
- add LinkedIn link
- improve readability ot Terms of Service link in dark mode

package-lock.json

@@ -31,7 +31,8 @@
         "gatsby-transformer-remark": "^5.19.0",
         "gatsby-transformer-sharp": "^4.19.0",
         "react": "^17.0.2",
-        "react-dom": "^17.0.2"
+        "react-dom": "^17.0.2",
+        "react-icons": "^4.7.1"
       },
       "devDependencies": {
         "@types/node": "^17.0.45",
@@ -17992,6 +17993,14 @@
         "react": ">=16.3.0"
       }
     },
+    "node_modules/react-icons": {
+      "version": "4.7.1",
+      "resolved": "https://registry.npmjs.org/react-icons/-/react-icons-4.7.1.tgz",
+      "integrity": "sha512-yHd3oKGMgm7zxo3EA7H2n7vxSoiGmHk5t6Ou4bXsfcgWyhfDKMpyKfhHR6Bjnn63c+YXBLBPUql9H4wPJM6sXw==",
+      "peerDependencies": {
+        "react": "*"
+      }
+    },
     "node_modules/react-is": {
       "version": "16.13.1",
       "resolved": "https://registry.npmjs.org/react-is/-/react-is-16.13.1.tgz",
@@ -35124,6 +35133,12 @@
         "react-side-effect": "^2.1.0"
       }
     },
+    "react-icons": {
+      "version": "4.7.1",
+      "resolved": "https://registry.npmjs.org/react-icons/-/react-icons-4.7.1.tgz",
+      "integrity": "sha512-yHd3oKGMgm7zxo3EA7H2n7vxSoiGmHk5t6Ou4bXsfcgWyhfDKMpyKfhHR6Bjnn63c+YXBLBPUql9H4wPJM6sXw==",
+      "requires": {}
+    },
     "react-is": {
       "version": "16.13.1",
       "resolved": "https://registry.npmjs.org/react-is/-/react-is-16.13.1.tgz",