satellite/web: replace cancel with back buttons

This replaces "Cancel" with "Back" on Clear, Create and Switch steps.
It also removes margin-top from the button rows in Clear, Create steps.

Issue: https://github.com/storj/storj/issues/5463

Change-Id: Ib2ef0dba9b91e82a7cf5b042fad0162128fa071a

web/satellite/src/components/modals/manageProjectPassphrase/ClearStep.vue

@@ -10,7 +10,7 @@
         </p>
         <div class="clear-step__buttons">
             <VButton
-                label="Cancel"
+                label="Back"
                 width="100%"
                 height="48px"
                 :is-white="true"
@@ -78,7 +78,6 @@ function onClear(): void {
         align-items: center;
         justify-content: center;
         column-gap: 33px;
-        margin-top: 20px;
         width: 100%;
 
         @media screen and (max-width: 530px) {

web/satellite/src/components/modals/manageProjectPassphrase/CreateStep.vue

@@ -10,7 +10,7 @@
         </p>
         <div class="create-step__buttons">
             <VButton
-                label="Cancel"
+                label="Back"
                 width="100%"
                 height="48px"
                 :is-white="true"
@@ -77,7 +77,6 @@ function onNext(): void {
         align-items: center;
         justify-content: center;
         column-gap: 33px;
-        margin-top: 20px;
         width: 100%;
 
         @media screen and (max-width: 530px) {

web/satellite/src/components/modals/manageProjectPassphrase/SwitchStep.vue

@@ -19,7 +19,7 @@
         />
         <div class="switch-step__buttons">
             <VButton
-                label="Cancel"
+                label="Back"
                 width="100%"
                 height="48px"
                 :is-white="true"