Make custom network fields readonly when its set as default

[srirambv]

Description

To avoid confusion of being editable, when a custom network is set as default, make the fields readonly so user doesn't try to edit it.

Steps to reproduce

1. Install 1.37.42 nightly build
2. Create a custom network entry and set it as default
3. Open Wallet Settings from Wallet menu and select network
4. Tap on the network to open details
5. Tap on a field, brings up keyboard to edit but doesn't allow to save it

Actual result

Custom network fields look editable but can't save it when its set as default network

Expected result

Make custom network fields readonly when its set as default

Issue reproduces how often

Easy

Version/Channel Information:

• Can you reproduce this issue with the current Play Store version? NA
• Can you reproduce this issue with the current Play Store Beta version? NA
• Can you reproduce this issue with the current Play Store Nightly version?Yes

Device details

• Install type (ARM, x86): ARM
• Device type (Phone, Tablet, Phablet): all
• Android version:all

Brave version

1.37.42

Website problems only

• Does the issue resolve itself when disabling Brave Shields? NA
• Does the issue resolve itself when disabling Brave Rewards?NA
• Is the issue reproducible on the latest version of Chrome? NA

Additional information

cc: @SergeyZhukovsky @Pavneet-Sing

[Uni-verse]

Verified on Samsung Tab S7 & Samsung GS 21 running version 12 using

Brave	1.41.94 Chromium: 103.0.5060.114 (Official Build) (64-bit) 
Revision	a1c2360c5b02a6d4d6ab33796ad8a268a6128226-refs/branch-heads/5060@{#1124}
OS	Android 12; Build/SP1A.210812.016

Use Case 1: Add custom network via DApp (chainlist.org)

• Confirmed custom network is readonly when set as active
• Confirmed user can edit network and submit new changes when its not active
• Confirmed when custom network can be edited will be indicated by the 3 dot menu

Use Case 2: Manual entry of custom network

• Confirmed readonly when set as active
• Confirmed user can edit, remove and set as active when network is not default. New changes can be submitted.
• Confirmed when custom network can be edited will be indicated by the 3 dot menu

Use Case 3: Upgrade with existing custom networks

Precondition: Installed 1.40, setup wallet and navigate to chainlist.org. Connect and add multiple networks and set a custom network as active, then proceed to upgrade to 1.41

• Confirmed existing networks are retained as well as active status
• Confirmed all networks that are not active are editable
• Confirmed user is able to edit, remove and set as active custom networks post upgrade

Network Info	Custom Networks