Add id with auto increment to pending contribution

[NejcZdovc]

We should add id in pending contribution table. This way we don't need to send 3 params to determinate which one is which. It's also less error prone as in theory we could have record with the same 3 keys, meaning we would be deleting too much data.

[GeetaSarvadnya]

Verification passed on

Brave	1.4.86 Chromium: 80.0.3987.87 (Official Build) beta (64-bit)
Revision	449cb163497b70dbf98d389f54e38e85d4c59b43-refs/branch-heads/3987@{#801}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Verified the test plan from Adds id to pending contributions table brave-core#4177
  

• Verified on both clean and upgraded profile
  

Verified passed with

Brave	1.4.91 Chromium: 80.0.3987.116 (Official Build) beta (64-bit)
Revision	dc00a510e4c2ae25c4d084cc3d946fc782249224-refs/branch-heads/3987@{#917}
OS	macOS Version 10.14.6 (Build 18G3020)

• Verified test plan from Adds id to pending contributions table brave-core#4177 for a clean profile
  • Verified for both one time and recurring (monthly) tips
  • Verified both display in pending contributions table in UI
  • Verified both display in pending_contribution table in DB
  • Verified both types can be deleted from table in UI

• Verified test plan from Adds id to pending contributions table brave-core#4177 for a profile upgraded from 1.3.118
  • Verified for both one time and recurring (monthly) tips
  • Verified both display in pending contributions table in UI
  • Verified both display in pending_contribution table in DB
  • Verified both types can be deleted from table in UI

1.3.x:

1.4.x:

Verification passed on

Brave	1.4.93 Chromium: 80.0.3987.116 (Official Build) (64-bit)
Revision	dc00a510e4c2ae25c4d084cc3d946fc782249224-refs/branch-heads/3987@{#917}
OS	Linux

• Verified test plan from Adds id to pending contributions table brave-core#4177 for a clean profile
  Verified for both one time and recurring (monthly) tips
  Verified both displays in pending contributions table in UI
  Verified both displays in pending_contribution table in DB
  Verified both types can be deleted from table in UI

• Verified test plan from Adds id to pending contributions table brave-core#4177 for a profile upgraded from 1.3.118
  • Verified for both one time and recurring (monthly) tips
  • Verified both displays in pending contributions table in UI
  • Verified both displays in pending_contribution table in DB
  • Verified both types can be deleted from the table in UI